You will need some type of operating system to put back on there. It will either need to be a copy of XP or it could be linux (which most *distros* are free from the internet). A gold copy which is what a stand alone copy of
Microsoft Windows XP Home Sp2b 1pk w/Upgrade Coupon for Vista - OEM is called (one that you buy separately from the computer) typically runs about $90.00 but it is yours and can go on any computer. One that is installed on the computer and is bought WITH the computer has to STAY on the computer so if the computer dies, so does that copy of XP.
Oh, and I FOUND all MY hard drives now. Liz