What kind of recovery CD's do you have? Any at all?
Some systems have a recovery partition on your hard drive. It's up to you to make your own discs from this partition. Since your drive is crapped, it's to late do that now (if you haven't done it). You can likely call HP and order a recovery CD. They'll just need your system serial #.
Read this before ordering your Recovery Discs! (US and Canada Only) | HP® Support
It's a little more complicated if you go out and buy a retail copy of Windows, because you'll have to scour HP's website for the correct drivers.
Get a new drive, let us know what discs you got and we'll go from there. I'm sure some of us could even walk you thru over the phone. It's not to difficult and will save you $$$ over calling some Dork Squad.