There are zillions of free midi tracks for many many songs, and I have literally downloaded close to a thousand such songs, as I used to gig live over edited midi files that I got from the web (or built) and had then run the project through to export to audio, which gave me simple MP3 files with the benefits of better-grade soft synths than general midi, as well as the simplicity of MP3 versus midi.
 
So, if you were to post back with the name of a a song you are looking for, I could take a peek on the web for you  to see if I could find a suitable midi file for you.
 
 
Bob Bone

^^ As many alluded to in this thread re-creating is often much quicker route, and the MIDI files Bob mentions is about the best jump start you can get. Be realistic with expectations of these though, since some are well done, and some are not so good.
 
If such a MIDI file can be found, the easiest way to flesh it out is to open it with SONAR with no MIDI output devices selected (preferences)... this will open the file and insert TTS-1. From there, create a VSTi track for each instrument and shift drag/drop the MIDI from tracks in TTS-1 to the VSTi tracks. Tailoring the sound for each VSTi is probably the biggest challenge.
 
Alternate method (no suitable MIDI file available) is to insert the original song as an audio track and the VSTi tracks as above. Set the tempo map to align the project to the song (a bit more complex), and then record each piece with a MIDI controller real-time, and adjust using piano roll view (PRV). With a properly set tempo map (very important), you can also use copy/paste techniques to flesh out each tracks as many parts repeat (this speeds up construction considerably). Again, tailoring the sound for each VSTi is still required.
 
The above is a high-level synopsis of such a work flow, but is rather quick once you have done it a few times.

sharke
To get a clean drum track from a full mix would be like trying to get the toothpaste back in the tube.

ooohh boy he made my day!!

Jesse G

sharke
To get a clean drum track from a full mix would be like trying to get the toothpaste back in the tube.

ooohh boy he made my day!!

I like the description that I've given to others, it's like making a cake with flour, sugar, eggs, milk, oil, vanilla, baking powder, mixing it all together, baking it and removing the cake from the pan, then asking to remove the eggs from the cake.  
 
Given all that, there's a science and art to this 'unmixing' that folks who do remixing/mashups are pretty adept at.  First, as others have mentioned, see if there's a intro, outro, dub, remix version, acapella, bootleg, or even MIDI that might have the song elements you're looking for in isolation.  If you can get this, this is the way to go.
 
If not, then you have some tools and tricks to try.  If it's vocals, you can try phase-inversion tricks to either pull out vocals or attempt to remove them.  If it's other things, then you can get spectral-analysis software to help you out here.  If you have the version of Sonar with R-Mix, or got lucky with one of the closeout version of the full R-Mix, give that a try.  Also, I hear good things about IZotope's RX-2, I'll have to trial that and see how well it works on a project I'm trying.   Also, you can use EQ and filtering to better isolate frequencies, then use something like Audiosnap or Drum replacer and then at least get the groove and replace with similar-sounding samples.
 
Of course, it will not be perfect.  But it may be just good enough.  I know as I'm doing remixes/mashups, since other things get layered over it, it's not too bad, and actually, it can even add kind of a low-fi gritty edge to the mix.  
 
 

http://www.zynaptiq.com/unmixdrums/
 
If you don't mind shelling out the extra bucks, this might work or at least get you close enough to make Sharke's suggestion of using Drum Replacer less of a hassle.