FAT32 is an older file system, and Microsoft wants to move people away from it. NTFS is superior to FAT32 in almost every way, and there is no compelling reason for users to use it anymore. Converting NTFS back to FAT32 should be considered a last resort in all cases and mind it its not so easy doing this.
Unfortunately, Windows XP does not have a built-in tool to convert backwards, like one can to convert from FAT/FAT32 to NTFS. U can however use third-party tools , viz, Partition Magic allows you to convert an NTFS partition back to FAT32, but often conversions simply fail, or destroy data. Backing up your data should be your first priority however you choose to convert NTFS partition back to FAT32.
I give an easy method of doing this without using Partition Magic, U can use Partition Magic to do this also : BACK-UP your DATA FIRST!!
First off, delete the partition that you wish to convert. This is done by going into Disk Management: right click "My Computer" -> Manage -> Disk Management, which is found under the Storage section. Right click the partition you wish to remove, and click "Delete Volume". This will erase the partition. Once you have done this, you must re-create the partition. This is done by right clicking on an unallocated region of a disk, and selecting "Create Partition". Then click "Create Logical Drive". Bear in mind that Windows cannot format a FAT32 partition that is larger than 32GB. This is the case because FAT32 is terribly inefficient on volumes that are larger than 32GB's, fragmentation becomes a serious problem.
To format this new volume, right click it, and choose Format. Again, if the volume you wish to format is larger than 32GB, FAT32 will not be one of the options available to you in the drop-down box. You will have to create multiple partitions if you want to format a large drive as FAT32.
ABOVE ALL PLEASE BACK-UP YOUR DATA FIRST.