No, it grub did't mess up Windows the first first time
No, Grub plays nice. It will chain-load Windows just as it did before. I personally use Knoppix for my critical-computer care needs, but look around, there are several options to choose from.
I had to reinstall Windows on my laptop for my web design needs, and then I had to go back and reinstall Linux. For me, it was a matter of partitioning properly. If you have space to shrink your ntfs drive, you can create a FAT32 partition, which can be accessed by both Linux and Windows. (defrag and backup your Windows data first)
I also ALWAYS create a separate partition for /home at least. With my personal files untouched, reinstallation was not painful.