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I have not really tested FAT/FAT32 yet as I don't use these 
filesystems now.

The Disk Defragmenter tool in Windows 2000/XP shows the number of 
files/directories fragmented in its report.

NTFS does handle growing files, but the operating system can only do 
so much without knowing the size of the file. Extracting from 
archives consisting of only several files does not cause 
fragmentation. However, if the archive has many files, it is much 
more likely that the default algorithm will fail to allocate 
contiguous clusters for some files. It may also depend on the amount 
of free space fragmentation on a particular partition and whether 
other processes are writing to other files in the same partition.

Some details of the cluster allocation algorithm used in Windows can 
be found at http://support.microsoft.com/kb/841551.