Yeah, if he defragmented three weeks ago, then it shouldn't be a fragmentation issue, unless there's some really weird stuff going on with virtual memory... but that doesn't explain the extreme slowness of a decently fast system.
Ruatha is right about disabling most stuff in MSConfig. You can disable almost everything in the startup tab and still have a workable computer, just without some features. Basically what you won't want to disable are the AV and Firewall processes, the video drivers for the higher-end video cards (if it's an nVidia card, it will start with Nv, if it's ATI, it will start with ATI), you might have something called mobosync which is basically a hardware monitor, and other than that, everything can be ditched. If you really think something might be important, paste the name of the program file (eg. tfswcrtr.exe) into google, and see what it says about it.
Also, when you're starting up, hit Ctrl-Alt-Del and bring up the Task Manager. Go to the processes tab, and sort by CPU. Post here with the processes that are taking the most CPU time and percentage, and we should be able to help speed things up.
And, pick one AV program, ditch the rest. Uninstall all of them, re-install the one you're going to stay with. Even if you aren't running all at the same time, the definition files interfere with each other, and it's an overall bad idea. Four isn't any better than one
Re: OT: Windows Optimization?
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