I'm working on a percussion piece, and much of it will be live instruments. But I'm not going to record entire parts, rather I'm going to find specific hits I like and then create patterns out of that. I could take the tiny audio clips that represent the hits I want and copy them to the beats I need, but that's a very laborious process and therefore not conducive to getting the creative juices going and experimenting. So I'm sure there's a feature in Sonar whereby I can assign an audio clip to a Midi note or something, and then trigger it just like it were a regular Midi note, and I'm happy to look up how to do it, but I don't know what the feature is even called, so I can't even look it up. Could someone point me in the right direction?

Session Drummer?

Ah, so it is. I see. OK, so then I can just record whatever sounds I want and then assign them to drums in a Session Drummer instance? Is that the best practice, to record them in a track in Sonar, export a clip as a wav, and then assign the wav to the drum? Am I limited to the number of drums in my kit (looks like 12 slots)? Can I assign different wavs to different velocities or anything?

Another solution is the tx16wx sampler.  It is both free and excellent!  I have used it to create vst instruments of some old outboard gear that I use.  It is also comes in 32 and 64 bit flavours. 
 
http://www.tx16wx.com

Look at the Matrix.

Drum replacer is pretty cool.

DropZone? Is it included with any modern Cakewalk programs?

If you are manually slicing created wav files (semi-painful), another thing you may want to try is FXpasion's Geist. Not only does it have a built-in slicer for pad assignment, but also a powerful step sequencer to allow up to 24 patterns per "kit." IIRC, the trial is fully functional for 10 days.

sharke
Look at the Matrix.

Thanks for everyone's ideas. While I'm not likely to buy anything, since this is all in the name of a single song, I have done some research and learned about the obscure little plug-in called sfz which ships with Sonar and does a little of what I want, though it appears I can only load a single wav. I then learned about .sfz and .sf2 files, apparently two flavors of the same thing, and a tool called Polyphone which allows me to create them using samples. This was very promising at first, as I grasped how it worked fairly quickly and created a test .sf2 file. And while sfz claims to be able to import sf2 files, it wouldn't recognize the one I made with Polyphone, however. Maybe Session Drummer will allow me to import an sf2 file I create with Polyphone. I'm getting there slowly.