You mean "Is there any way to use left-click in Windows XP?" because Boot Camp is just a drive partitioning tool/driver creation that you only run once that allows you to install Windows. Once that's done you never use Boot Camp again because you have a fully fledged PC.
The single button on the MacBook Pro works as a regular left-click in Windows XP, if you've used the most current version of Boot Camp to burn your driver CD then the drivers in there should map the right command key (either on it's own or in conjunction with clicking the mouse button, I don't know) to the right-click function in Windows.
the long answer:
be it bootcamp, or XP or OS X or anything... click the button on the MBP gives you the effect of left click.. now if you want to right click, in OS X (and as previous poster said, bootcamp an application in OS X) you do control click, and in XP, you do right apple+click after you installed the disk.