wysiwyg, I had to format from manufacturers recovery cd's after I'd changed the file system to NTFS, and wanted to go back to FAT32 as it's faster (ok that's another debate). Don't know if your drive is partitioned, mine was, so I copied all that I needed to C, then formatted D using recovery cd's. Then put what I wanted on D, and formatted C. All hunky dory now back on Fat32, so you should be able to do it as aisleman suggests, just back up everything you need first.
ps. Remember, any window updates, patches, driver updates etc will need reloading afterwards.
Edited for ps.
