ZDNet offers a nice video clip which shows, how to remove Windows 7 and Vista from a dual boot environment
QUOTE
July 8th, 2009
Remove Windows 7 or Vista from a dual-boot configuration with the Bootsect command [video]

Posted by Larry Dignan @ 2:20 am

Dual-booting Windows is a handy way to test betas and service packs before committing to a new OS. But once you’ve made your decision to stick with the new OS or give it the boot, you’ll likely want to get rid of those extra partitions and revert to a single O-S. If you don’t want reformat the hard drive and completely re-install your chosen operating system, there is an alternative. In this IT Dojo video, Bill Detwiler shows you how to use the Windows Bootsect command to extract Vista or Windows 7 from a dual-boot configuration with Windows XP.

More:
http://blogs.zdnet.com/BTL/?p=20797