Gronk, are you letting it boot until it asks you for a password? Or are you interrupting the boot?
If you're waiting, you will need to get a new copy of the Windows install media (can download from windows.com) on either a CD or a USB. Interrupt the boot (normally by pressing F12 or F9 on most computers) so you can select where to boot from. You have to be pretty quick to see which button to press, but the positive is once you see it, just press it repeatedly as soon as you power on the PC and you'll trip it and open the boot menu.
When you've done this you just walk through the install process and you can format the drive as a part of this. You'll lose all data that was on the computer, but you've already said you don't care about that. You might have to re-install some of the device drivers once you've installed the fresh Windows OS, but that's pretty easy to do.