Yes, I only have Vista and the big WoW folder on the HD. I use Windows only for gaming, and my only gaming (not on the PS3) is WoW currently.

Resizing the Bootcamp partition might be possible, but it is not a direct MacOS functionality. You could certainly use a Bootcamp backup utility (like Winclone, that's the one I use) to make a complete backup, resize somehow, and then re-inject your windows image, but it will probably not be that trivial.