I highly recommend Sound on Sound's Synth Secrets series to anyone interested in basic synthesis techniques. It's geared toward the analog synthesist, and here in computer-music-land we have far more possibilities, but a good grasp of the basics of analog synthesis is useful for any electronic musician.
This snare drum was based on Sound on Sound's description of the Roland snare sounds. It's not an emulation of a Roland drum machine sound, though -- all the parameters were tweaked to satisfy my personal idea of a good snare sound.
Sound samples: ogg mp3
If you want to be able to connect a [metro] and get realistic-sounding drum rolls, you might want to randomly change some of the numbers in this patch with each hit.