Already have Boot Camp XP, would like to add Linux

I have two older macbooks (back when there were macbooks AND macbook pros, now there are just macbook pros). I have OS snow leopard on both of them although the processors are a little different from being a year apart. I believe one is 32 bit and the other is a "duo" which can handle 64 bit.
Due to the 2 gig ram restriction, I am staying with the current operating systems.

I currently have have windoz xp bootcamped on both of them along with the many programs I have installed over the years , all of which work fine. As I see more and more software opening up for Linux (or is it called called Ubantu?), i would like to try it out without disrupting my current setup.
Is there any way I can add a partition for Linux boot without having to lose or reinstall windoz xp, which would be a major pain.

Alternately, with thumb drives becoming super huge these days, would there be a way to do a linux boot and run off of a thumb drive?

Thanks
K

Thought I would ask again.

thanks
K