installing a new hard drive?

I am going to buy a new hard drive to put into my compaq (brand new). Do I have to buy Windows to install onto the new hard drive, or can I use the restoration discs made from my current hard drive?

You can use the restoration disks. Are you adding the hard drive or replacing the old one? It would be a good idea to keep both. Never can have too much storage.

Recovery disks should work. How old's the compaq? Some have part of the Bios on the main harddrive so you won't be able to do anything without the old drive as the primary.