I want to be able to play and record my Yamaha electronic drum set and a  keyboard at the same time. The drum module has midi out and right and left out. I've been recording the drums using right and left and an armed midi track (muted) for some time now and it works great. I have a Tascam us1641 that has midi in and out. the key board also has midi in and out. I guess my question is what would I need to do as far as routing to have the drums (midi out) and keys going at the same time? I've never seen an interface with multiple midi inputs but surely this is not a strange thing i'm trying to do.

I would imagine that sort of thing would be covered in the user manual.  Most manuals seem to be posted online, if you don't have a hard copy or electronic version saved on your computer.  :)
 
Virtually every single one of my keyboards (those with on-board sounds as well as midi out), allowed the simultaneous playing of live sounds through the audio outs, at the same time also sending midi data out through the midi out or USB cable to trigger sounds elsewhere or record the midi.  I don't see why your situation would be any different.
 
Good luck with it.
 
Bob Bone
 

That makes sense. I might not have been clear... how would I physically plug two midi cables into my interface with only one midi in? would a midi to usb  cable / adapter solve this?

You'll need a midi merge box like this 
 
I used to have my Drum machine going and play the keys at the same time, I also used it to have midi sync clocking the computer and so on. Handy device. 

That's what I'm talking about. More of a physical splitter or merger in this case. Now I just have to figure out how to tell the daw to split these signals back where they belong. Of course I'll have to get a merger first! I'll probably be back, Thanks guys

There's a few way to split the midi channels after the fact like with CAL,
but... I "think" you can insert 2 midi tracks and then instead of using OMNI set each channels input the same as the  midi source.  Say channel 1 and 10. 
Pretty sure this will work as there would be no reason to offer us sperate channels in the first place. 
There must be people here who have dumped multi track midi sequences live from a player in the past. 
 
Only other solution I can think of would be to see if 2 dedicated midi devices like those MIDI Sport's can be used along with an audio interface. But I doubt the drivers would cooperate. I would confirm that with someone who's got it working first.

Yes channels! I will try to config when I get the hardware
 

If either the keyboard or drum module has a THRU port (or THRU mode for the OUT port), you can "daisy-chain" them into one port without having to get a separate merger.
 
Also more recent keyboards usually have a USB MIDI port for which a driver will be loaded in Windows that presents the keyboard's MIDI ports to SONAR like any other MIDI interface so you don't have to use the MIDI DIN cable connections to your interface.

And I also was wondering about the keyboard and the Yamaha drums and which models they are as my Yamaha drums do use USB which you are correct have a different driver which has nothig to do with my ASIO drivers and happily co exsist. So that is a great idea given that is an option.  
If both instruments have USB then it's problem solved. 
If they are both midi only then it's back to the merge box. 
For me trying to use a thru port I always ended up with wierd things like missing notes as well as there can be added latency which is why I bought myself the merge box as well as a Roland A880 a long time back.
Of course the OP can always try that and it might work, but he did say the drums are midi out and not usb so let's see what they say.. 

If you are near a music store - could you perhaps bring your keyboard to the store and get some guidance from them on how to get your particular setup working?
 
Just a thought,
 
Bob Bone