I didn't know Windows 7 was in beta already. I'm gonna have to give it a test drive. If the Vista betas are anything to go by (and they may well not be since Vista was an entirely new framework) then there could be serious stability issues in the new betas.

Also, in order to easily install a Vista/XP dual-boot, make sure you install XP first. This way the Vista installation is able to detect the presence of XP and will contain entries in the bootloader for both operating systems, whereas it doesn't work the other way around.