Hard disks get priority over other devices which is why it bumped the CDROM over to F. They also have to be labeled consecutively from C onwards. You can't change the ordering of hard disks.

I don't think there is any easy way of telling everything that the CDROM drive is now F apart from reinstalling and search and replace on the registry...

Back in ye (yes, I know ye isn't a real word) olde days, I tried to keep the CDROM drive at a higher letter that what was automatically assigned so it wouldn't have this problem. But now that everything starts setup by booting off the CDROM it's harder to do.

- Trevor