Well yes, and no. If you have your hard drive partitioned to A and B, and you boot on A, and right click on B in My Computer and format it that way, you will format only B. It's impossible to format a drive you are booted from. If you boot from an external drive, and you format the overall drive (as in the physical hard drive, not the software partitions), then you will format not only both partitions, but you will lose the partitioning as well (it will become one single drive again). Like I said, it's impossible to format a drive you're booted from, so if you want to only format one partition, just boot from the other to do it. If it's 1 OS and 1 data partition, and you only wanna format the OS partition, then boot into like Linux for example (since most of the big distros offer liveCD functionality) or boot from an external drive, and make sure you use some sort of partitioning software (e.g. Gparted [which there's a liveCD of Gparted]) to format just one partition, just to be on the safe side.
