defrag your HDD... you'd be surprised at just how much speed you can gain.
Also converting your current disk form FAT32 to NTFS is a very good option (but make sure you backup your important data safely on another drive just in case)
as for the Overclocking you have to actually set the cards clock, set apply on reboot then reboot your machine so the BIOS itself clicks in the new clock frequency.
That said the 3DMark03 doesn't actually allow nVidia cards to be overclocked whilst your using it - dunno why just doesn't allow it.
4,330 isn't too bad to bad from the 'mx' version if you had a ti i'd say to expect a good 1,000-1,500 extra ontop of that ... but for your current card its pretty good
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as for your activation problem, there are quite a few tech sites that explain howto alter your version of Windows between each of the versions when you copy the CD - if you change its serial to XP Pro you then don't have to worry about activation.
It's what i did with my XP Office Standard because it bugged me that i spent like $30/month on phonecalls simply to reactivate the stupid thing.