Umm...your question isn't very specific but ill try to cover what your trying to say.

If you are trying to convert FAT32 to NTFS, for one you have to have either WinNT,Win2K, or WinXP as your OS(will not work for Win9x).
If you do have one of these as your OS then type the following command at the command prompt:

convert  c:  /FS:NTFS

On the other hand, if you are trying to convert NTFS to FAT32, I am afraid that you cannot do this. The only way to put your drive back to FAT32 is to boot up the windows2000/XP CD and use it to delete the existing partitions during partitioning phase of the installation process(leaving the drive all 'unpartitioned space') and then recreate them as FAT32. Then continue installing the OS.

hope this helps.