A few months ago I installed CentOS on my laptops second hard drive. During this process it installed GRUB as my boot loader. Since the inital installation I have not booted back in to CentOS at all, so I removed the linux partitions from the second drive and hoped for the best. I was so wrong.
Removing those partitions removed GRUB as well, so my laptop (now my main computer) would no longer boot into Microsoft Vista Home Premium. To fix this I used the Vista DVD to boot into Windows Recovery Environment (Windows RE) and used a tool new to me Bootrec.exe.
Microsoft has a very handy article on how to use Bootrec.exe to fix just such an occasion. For my situation I had to use the /fixMBR switch and reboot. It was literally that simple!