The NTFS file system is more stable than FAT32 and can read anything from a FAT32 file system-but not vice versa so I cannnot understand your need to do this.
However there is a way of converting NTFS to FAT32 without reformatting but I am not sure if it works in reverse.
The method is:- Open up a command line in the Run Box by typing cmd.
In the command line type :- convert c:/fs : ntfs and then hit Enter (you would obviously need to replace ntfs with fat32 )
Then reboot.
If this doesn't work then obviously you will need to do as vhg advises.
I have done this before by simply going to 'My Computer', right click on the drive and select Format.Type in FAT32 and click start.If memory serves me correctly, it takes about 20 minutes to complete, but as others have said, you will lose all data on the drive.