[andrewas]

This is because MSDOS cant see a NTFS partition.

Try format c: just in case, dos knows there is a partition there, it just cant access it.

Otherwise, use FDISK, delete and recreate the partition. DOS can definately format an empty partition.

Of course, if your planning to reinstall XP (Or in fact any sophisticated operating system (anything other than windows 9x basicaly) you can partition and format the drive during the installation procedure.