Your powerbook should have an internalized mic (depending on it's age), you just may not know about it. You can check in the sound section of system preferences. If it actually doesn't, then you can hook up any external mic.
As for a webcam, I use
iusbcam to make my logitech notebook cam work on a powerbook g4. Cheap program, works great. Check out their list of compatible cameras. I was able to get one that works fine at wal-mart or target for like 20 bucks.
Otherwise, any Firewire webcam will work, but good luck finding one that doesn't cost an arm & a leg.