I was looking for a way to kill running tasks from the command line in XP when I came across information about the command line utility taskkill.exe. This does the trick but isn't available in XP Home. It will work with XP Home however.
I found an unofficial link to taskkill.exe here.
Alternatively you might want to check out another officially downloadable Microsoft utility called PsKill. PsKill will do the same job as taskkill.exe.
At the following link you'll find a description of PsKill and a download link for the PsTools suite that contains PsKill. http://technet.microsoft.com/en-us/sysinternals/bb896683.aspx
[ thanks for the tip Anonymous ;-) ]
If you're still determined to proceed with taskkill.exe, Here is Microsoft's documentation on taskkill.exe and here are some usage examples from Computerhope.