All the suggestions here are good, but actually Puppy Linux is also a good start. Try their latest BookwormPup64 release, it is very polished, solidly build, and most importantly small enough to install on you usb pendrive. Puppy linux runs in your ram, so it is super fast even on old basic hardware.

Give it a try… I start using puppy after my pc crashed… Never look back to windoz since then…