The Windows XP command line defragmenter is defrag.exe.

If you open a CMD prompt and type defrag /?, the following is displayed:

<b>Usage:
defrag <volume> \[-a\] \[-f\] \[-v\] \[-?\]
   volume drive letter or mount point (d: or d:\vol\mountpoint)
   -a     Analyze only
   -f     Force defragmentation, even if free space is low
   -v     Verbose output
   -?     Display this help text</b>