I have a laptop (XP) and would like to add two extra monitors onto it. I already have one monitor hooked up, but how would I add one more when my laptop only has one port?

There are several options. I suggest you look at Google, then come back with any specific questions you might have. In any case, the display on the 3rd monitor will be the same as the one it is split from.

Alternatively, you can get USB Video adapters, which does allow you to extend your desktop across the added monitor, but it depends heavily on your existing resources (CPU and RAM) so I don't how good the performance will be.