Way back in 2000 / 2001 I was an IT intern. My job was to do the really manual processes for a small department with in a much larger company. One of those was monthly defrags of all PCs and Laptops (if they where available). I had to go to each and every PC, log on, and start the defrag process manually. I believe this to be my first moment of "I should automate this". Problem was I didn't know how or really where to start. I knew script was the answer, but just couldn't get things to work. I believe I eventually created a scheduled task on each machine (by hand) to do this for us.
Fast forward 10 years and I am still in need of the same thing, as we don't have Vista or Windows 7 deployed. But now I have a much better understanding of what needs to happen and even better I know where to start!
PSExec, which is part of the System Internals PsTools suite is my answer these days. A simple script, run from my PC (still manually for the time being) is able to handle defragmenting all of our PCs.
psexec @C:\Updates\Comps\AppPCs.txt -n 10 -c -f -d JkDefragCMD.exe
I use the files with PC names to speed up re-deployment of everything. The -n 10 flag tells psexec t0 wait 10 seconds before it times out the PC, instead of 60 (I believe this is the default). -c copies the file (jkdefragcmd.exe) to the remote system. The flag -f forces copying, even if the file exists. The flag -d doesn't wait for the process to terminate, this is as asynchronously as I can do.
My next step is to hook this up to task scheduler and have it run the first Sunday or something.