The only way is totally destructive, you must reformat back to Fat32.
To ReFormat Back to Fat32
To do this boot from XP CD. Do not enter SetUp, instead press R to go to the Recovery Console. Select your XP installation (usually only one) press 1 and Enter. Type administrator password. You will be placed at C:\Windows> Type format c: /fs:fat32 and press Enter.
It is possible to convert from NTFS back to Fat32 without losing data using Acronis Disk Director suite. The advice is to make a back up first in case of problems but it should be OK I have used it on a couple of ocassions with different machines (only because I wanted to access data from Linux, if I was staying with windows i would always use NTFS).
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