System freezes up momentarily while booting up XP, but not at any other time

Strange thing going on here that wasn't always the case...

When I start up XP (Parallels 4, OS X 10.5.5 on MacBook unibody), at the black XP booting screen, my system seems to come to a halt. The cursor becomes very slow and jerky and eventually stops responding entirely. It does this for about 20-30 seconds and then unfreezes and continues.

I thought it might be something to do with HD-intensive activity, but when Windows is past the boot screen, no amount of HD-intensive activity will reproduce this effect.

Any ideas what's going on?