The Windows XP command line defragmenter is defrag.exe.

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

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