I think the OP may be looking more for a simple audio editor like Cakewalks "Pyro" Audio Creator 1.5 than a DAW
It has mp3 conversion/export
http://www.cakewalk.com/Products/AudioCreator/feature.aspx/Convert-using-pyro-Audio-Creator

IDK about the MP3 encoder stuff but it seems weird the plugin scan is taking so long every time you open Sonar. The first time after install or adding a new scan location takes a little while (and I mean a LITTLE while like well under a minute) but after that it pretty much just pops open.
 
Did you ever end up upgrading your system? I seem to recall you were running some very outdated stuff.
 
Ah and looking your specs they still say XP on a P4. Is this still true? XP is not support and a P4... well my P4 is long retired (although I still have it set up but I've locked it to the old programs it contains... wouldn't even try to run X2 or even X1 on it).
 
And yeah... as others have mention use the MP3 export option within Sonar. You are taking the scenic route through Cracktown.
 
Edit: Of course I totally overlooked the i7 section of your sig. Sorry. So yeah... scans shouldn't be taking that long. Pyro works but if you have the encoder a direct export from Sonar should be pretty simple AFAIK.

Pyro is $20 in the store.
http://www.store.cakewalk.com/b2cus/ProductInfo.aspx?productid=10-CWAC1.00-10E

I think Pyro is 32-bit though. Not sure what, if any difference that makes. I bought it mostly to create mp3 libraries because I hate the latest MS Media Player. In fact I've always hated Media Player. Hoping Pyro will behave more like WinAmp... and I can add VSTs to make some of my crummy old punk/metals album collection sound less like I'm listening to it inside a tin can (whoever produced the early DK stuff needs a slap).

@Beepster - Vlada maintains multiple computers.  I believe the XP one is there if needed for some of the older hardware she has - but my memory is a bit fuzzy on the details of her setup.
 
I had talked her into building one - hopefully she is happy with that choice.
 
But I do know she has some complicated needs, and I am not sure I understand her setup anymore, but will try to help if I can.
 
She had SIGNIFICANT prior hardware/software trauma, but much of that went away (at least until now) with her new computer.
 
Bob Bone
 

Hi, Bob. Yeah the sig confused me. My mind's all over the place. I remember the XP/P4 woes that were going on with her. Seems similar to some of the issues I was having when I wanted to move into more modern DAW stuff. My old rig just wasn't up to snuff but I still wanted to retain the programs/files on it (which has already paid off in terms of yanking old tunes off of and there is a lot more to do before I rip it apart and try to fix some issues it is having like what I presume is a failing video card). I was hoping to keep that rig going but after some research I realized I was fooling myself and built the new rig (which completely destroyed my finances but was worth it).
 
Sometimes you just gotta sink the cash into stuff.
 
Hope you've been well. Cheers.

Thanks - Beepster, a friend of mine took me last night to see Steve Morse Band and Joe Satriani last night, so other than recovering from the physical toll that took on me, I had a GREAT time.
 
I even got to talk for a few minutes with Steve's bass player, Dave LaRue (was also in the Dixie Dregs with Steve).  Dave is a phenomenal bass player, and is also playing in a band with a guitar-playing friend of mine - along with Rod Morgenstein (also formally with the Dregs).  I am HOPING beyond my wildest dreams that I would get to do some keyboard tracks for either my friend Brian (the guitar player), or for Steve.  One can only hope that 48 years of getting ready for it is enough time :)
 
Vlada has done a remarkable job of digging into the middle of all of the new hardware, as well as her new OS, a Sonar upgrade, and all of the new software, all the while keeping a GREAT handle on making sure her vast army of old-school keyboard synthesizers all play nicely in this brave new world of hers.
 
HOPEFULLY, we can 'twixt us help get her issues sorted out.  She has been through the WRINGER in the past with trying to remain productive in a sea of crashes.
 
Bob Bone
 

Beepster
I think Pyro is 32-bit though. Not sure what, if any difference that makes.

It does not make any difference. 
 
Using Sonar to transcode MP3 from standard wav files is like using an ocean liner to get to the grocery store.
 
 

Yup - I always convert things outside of Sonar, although I will export straight to MP3 if that is the end-format I am aiming for.
 
Vlada, the Cakewalk MP3 component is for ENCODING, not for converting.
 
Bob Bone
 

The only complaint I have re the MP3 encoder in Sonar is how it handles creating VBR files. Many is the time I need to use a 3rd party app to correct the VBR data in a Sonar created VBR MP3. Usually seen when you open said MP3 and see the length is 23 minutes when it really is only three 0 five!