is there some software out there that can accept midi knob signals and turn the number sent (0-127) into an amount of milliseconds thereby signalling a rate for a sample (wav maybe) to play? it'd be nifty if i didnt have to program this stuff myself.

If you mean that the percussion sample would be looped and you'd use a knob to determine the length (in milliseconds) of said loop, Reaktor can do that, but if you want it to be like a beat, and you're not looking for cool ass Aphex Twin style rolls, programming it into a sequencer via a softsampler would be a lot easier. Reaktor can also be a good softsampler for that kind of traditional playback type of stuff, but if you're not interested in all the crazy stuff Reaktor does, then there's certainly cheaper soft samplers out there.

it's free since a year or so...
http://www.geocities.com/midibrainz/