Remember that this is beta software and that Apple is not offering support. If you must live on the bleeding edge and already have BC installed just run the 1.0.2b1 installer, burn a new driver CD, boot into XP and install it. As reported by MacFixIt:
Unfortunately, Apple has provided no documentation regarding enhancements in this release. The disk image download itself has a modification date of July 10th (yesterday) at 9:17 AM, but the files therein -- including BootCampAssistant.pkg, the installer for the Boot Camp Assistant -- carries a modification date of June 19th.Details as what has changed in the 1.0.2b1 update are non-existent right now (Apple didn't publish a change log) but you can find out more if you keep your eye on the Apple Discussion Boards. Specifically this thread.
It is presumed that this update includes revised versions of the Windows XP Mac drivers, so you should burn a new drivers disk (using Boot Camp Assistant) after installing the Boot Camp update, then boot into Windows XP and re-install drivers.