New OS install, no hard drives showing up

I'm installing Windows 7 on an older PC. It was running on it before but my hard drive bit the dust. When I boot from the install disk and go to install it, there are no hard drives listed and the message says "No drives were found. Click Load Driver to provide a mass storage driver for installation."

It's an old Dell Dimension 8300 with a couple WD hard drives in it, a 250GB and a 500GB. I could get the model numbers if that's necessary.

Thanks in advance,
Nathan