And of course your software's limitation. Granted that you will usually run into your hardware limits first before you hit the software limits.
Pro Tools LE and M-Powered are limited to 32 recorded (18 simultaneous) tracks (48 if you get the expansion kit) and 256 MIDI tracks.
There's a free recording app called Audacity (for those people that are running pirated stuff and don't know how to use it anyway... just ditch it and start learning on Audacity) It's a simple straight forward multi-track/overdubbing program. Runs on anything, Linux, XP, OSX. Upto 16-tracks. And it's really free. Google it!
I'd recommend this to anyone who's just starting out. You get to learn the basics of recording (it can handle up to 96/32FP) without a lot of the extra functions that you probably won't need just yet.
This program is perfect for those that just do overdubs and don't have multi-channel soundcard inputs. Just press R to record, and SPACE to stop.