If you are going to buy a new hard drive get the biggest one you can affort because in a couple years it won't be big enough!
A few years ago the first hd I bought was 80 meg and cost about $500.00 USD. I thought it would last forever, but forever turned out to be about 6 months when I filled it up with MS-DOS 6.X os. I have bought several since then and MS-Windows seems to be getting bigger and bigger as hardware gets cheaper.