I had the same problem yesterday (I had formatted the Ubuntu partition which turned out to have had contained the Grub settings) and made it work again this way:
- Run the Windows install DVD
- Go to system restore options (I don't exactly remember what it is called) and choose command prompt from the list.
Execute the following command (replace [DRIVE] with drive letter):
bootsect /nt60 [DRIVE]: /mbr
Maybe it also works if you use "SYS" instead of a drive letter, I don't know.
This solved it for me, good luck.
Edit: Did some research on Google. It seems you can use "SYS" as well instead of a drive letter, the command can then look like the following:
bootsect /nt60 SYS /mbr"