FAT32 to NTFS - No problem
NTFS to FAT32 - You cannot do it*
*Without a 3rd party (i think)
Quicker to reformat and choose FAT32.
Use the CD and boot from that, do not use a boot disc. You can create, format partitions from XP setup.
The partition size has to be under 32GB for the XP setup to give the option of formatting in FAT32.