A friend of my purchased  Yamaha E-drums so I asked him to come by and see if he could use it to trigger Superior Drummer which I use with EZPlayer.  We got Sonar 7 Producer to recognize it quickly, but when attempting to have him play along with pre-recorded audio, the latency was so extreme it was impossible to do.  Now, I have never experienced any latency issues on my computer, even recording 8 tracks simultaneously. 
I am however, pretty much of  complete novice using midi, especially with external controllers, so I figure I must be missing something obvious.  Is there anyone out there who might have any ideas about how to deal with this?   

The best way to avoid latency when recording MIDI data from external sources is monitor the audio generated from the source. This eliminates the need to monitor through the DAW for the MIDI source (in this case the Yamaha E-drums). Use the audio output from the drum kit brain mixed with the playback of the other tracks from the DAW for monitoring while recording the MIDI from drum kit.
 
If you must monitor through the DAW, make sure the audio interface is setup for low latency audio recording. When using ASIO mode this will mean setting the buffers to 128 or less. Then make sure no plug-ins are used which add latency. Plug-ins with look ahead buffers like LP-64 EQ, LP-64 MultiBand, Perfect Space and TS-64 need to be avoided. Sometimes the best way to eliminate all the latency added by project plug-ins is bounce the whole project down to a stereo mix and archive all the individual tracks and disable the FX bins in the buses. Monitor the bounced mix when adding new tracks. When done tracking, delete or archive the bounce mix, restore the individual tracks and bus FX bins.

Thanks scook, I soloed everything but Superior Drummer and amped the e-drums and could play along just fine, even when recording.  But the playback, except for the 1st couple of drum kicks were WAY off time.  Right now I am running a midi out from the e-drums to my saffire pro 10 interface and firewire into the DAW.  Do I need to run a midi out from the interface back into the e-drums as well?    

There should be need to send anything back to the drums. What are your interface settings?

Which set of drums are they,?, I have the DTX 400, They use a USB connection and you need to install a Yamaha Driver first. There is a very tiny bit of latency that is easily dealt with the minute you quantize the new recording. 
I do as Steve has said and monitor using the Yamaha brain. I patch the Yamaha's outputs to 3/4 input of my interface so it comes through on both headphones and monitors. 
It also allows me to record the sounds from the brain if I so desire. But I will always edit the performance first. 
If you do use the MIDI connection then the Focusrite drivers are in control. Make sure you have them up to date and that the Focusrite is your timing master in audio preferences. 
 
 And as Steve has pointed out make sure you bypass all the effects bins while tracking midi. 
 

scook--the asio buffer settings were both for playback and recording set to 256.  I changed the playback to 64 and that helped some.  Also bypassed FX bins.  And, sock monkey, I did check and the Focusrite is the timing master.
As far as which drums they are, Id have to go back out to the studio to check.  They are not mine but belong to an actual drummer, which is good cause I cant play them.  (not the reason for the bad timing, just in case you were thinking that.  LOL)
Only invited this guy over because I thought it might be a quick way to get an actual drummer to get Superior Drummer sounding more real or intuitive for the song.  I think its rather a cheap set and I don't care much for the direct sounds it has, which is why I was thinking just a strictly midi input.
 
 

The solution: don't record while monitoring Superior Drummer. Record MIDI while monitoring the sound module that came with the E-drums. This will eliminate the latency issue while tracking, and you can then substitute Superior Drummer later. And yes, SD will sound better.
 
Even with a 64-sample buffer, the round-trip latency will still be greater than what a drummer is used to.

It should not be hugely delayed no matter what. If that is the case then those drums must be real old and are what is causing the problem. 
Or I see the Safire Pro 10 is a legacy product and there are no drivers on the focusrite site. So if your running XP 32 bit drivers and your OS is 64 bit that might explain the midi issue. To test you could borrow any midi keyboard and see if it behaves the same. 
 
My set the DTX 400 is the basic model made by Yamaha for last few years. They retail for $500.
There is only a tiny tiny bit of latency which is going to happen no matter what. 
It shows as my snare hits will be about 64th-128th note after the beat.
I fix this buy dragging the notes back by that amount, or I quantize to 32.  
They have made a huge difference to my drum tracks. I have been entering notes on a keyboard controller since 1985 and these drums are what I have always needed. So I encourage you to make this work. 
 
  I soloed everything but Superior Drummer and amped the e-drums
 
This is not exactly what you would do. Your still triggering SD which will be a tiny bit delayed. 
This bothers me as it sounds like I have digital delay on the kit. I know people with better computers and interfaces don't have this issue. But I've read a lot of posts where we all seem to use direct monitoring for better timing.
 I'll just explain what I do and hopefully it will work for you too. 
 
The song will already have either a click track or something to follow. 
Insert and MIDI track and set it's input to the MIDI port of your interface. 
You should be able to use Omni and the drums will transmit CH 10. 
Now here's the differance. 
I set the Output of the MIDI track to my interface MIDI out which has nothing plugged in. 
I do this instead of using "None", because Sonar often assigns new inserted tracks to your last synth. 
After you record the midi track you then assign it's output to SD and start editing.
 
Now there's a dozen ways to monitor but the main thing is you need use headphones or the monitors need to be as close as possible to the drummers ears. 
I would  plug the Yamaha brain output into inputs 3/4 of your interface and use the Safires monitoring options in the phones or speakers. 
The drummer needs to hear both the playback and the performance though the same system.
I guess that older Focusrite doesn't have Mix Control. 
 
 
 
 
 
 

Good suggestions all!   Thanks for taking the time to help.  Come this next weekend, I will try and implement what was said here and report back! 

Ok, I needed to get back to you great helpers to let you know that based on your suggestions, I was able to make it all work without a hitch.  No latency issues anymore, and the cheapo e-drums are driving Superior Drummer, so all is well.  Thanks again for your help.