How do I format my hard drvie?

I have a dell studio 15, a laptop, windows vista. I got a virus, and eventually, though I don't think due to the virus, my hard drive died. I managed to get all the data onto a external hard drive, but I'm afraid I must've collected the virus on there too. Anyway, I got a new hard drive for my laptop, made it a 500 instead of the 320 it had before. I put most everything back on the laptop and it was working fine, but then, I'm not sure if it's due to the virus or the new hard drive, but everything goes non responsive as soon as I click on it. I want to try to delete everything and be more careful about what I put back on my laptop. I REALLY don't want to spend any more money than I already have on trying to fix it. So is there a simple way to delete everything on my laptop? And I mean everything. I have all the starter discs and all my data saved, so that does not matter. Please lemme know, thanks!