I have a windows vista home premium computer, i had backed up the registry unfortunately after i had already done damage, is there away to restore it to default?

Notices come up that my home computer has been infected with a virus.

I live in California and called a well known company called the Geek Squad. They said the fee would be about 0.00 to clear it up.

Is that standard fee for home computer virus cleanup? Will pay it if I have to but seems high fee for this problem.

Any other suggestions on how to clean up my computer.
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how do i use it? ive backed up all my data on a external Ipod so please help its reinstalling windows xp pro

just put in new Hard drives and reinstalled windows xp home. in stalled all the drivers that came with my dell and i am online with my cable modem, but everything seems much slower?any thoughts on why this might be?
is there why to check and make all my setting and drivers are correct?

I have already installed other cleaners like "Registry Optimizer", "Regseeker", and "Registry Bot" so far they all find different problems and don't seem to fix or remove any of them. My OS is windows 98 and my computer is a Compaq and it is a little on the older and slower side. Any and all help would really be appreciated.