Alrighty, well, I went out and bought myself a new keyboard, partly because after about a year of typing on a cheap 10 dollar keyboard some of the keys got harder and harder to type on, and partly because my wrists were starting to hurt. So I went out and got a curved keyboard for 20 bucks. However, Microsoft seems to think that volume control should be done by 2 buttons, 1 up and 1 down. However, I've gotten quite used to the wheel my cheap one had, and I liked it as it gave me more of a quick 1 motion volume up or down. So I went ahead and ripped apart the old one and took it's volume control and popped it into a project box, the box is about 3 bucks from Radio shack, and the keyboard cost me 10 a year ago, so 13 bucks for a nice analogue volume knob still sounds like a deal to me.
Step 1: Get a cheap keyboard with a volume knob / use your busted one :)
Keyboard assembly is pretty simple, so I dunno if this should be a step.
However, just take all the screws out, and remove the controller board, which on the cheap keyboards is normally one board that has the 3 LEDs on it for the lock keys, and it'll also have a jumper cable headed over to a daughter board that has the volume knob on it. (I already stole the volume knob in this photo)