Ok yeah Vista and XP are plug and play however that is differnt to the bios. When you first turn your computer on it will come up with the logo of whatever brand computer you have bought. Down the bottom of this page there should be something that says press f2 to enter setup or press DEL the keystroke varies from computer to computer. This will give you access to your BIOS page.
Usually these vary from computer to computer as well as to the layout. but somewhere on this page there should be your Hard drive settings. If it is not on this main page try looking under hardware IDE devices etc.
Basically you are looking for a list that looks something like.
Harddrives
1. SATA Western digital 320GB
2. AUTO detect
3. AUTO detect
or
Harddrives
1. SATA Western digital 320GB
2. None selected
3. None selected
or
IDE Devices
1. LG CD/DVD RW
2. none/autodetect
3. none/autodetect
As i said how it will look will vary but what you have to do once you find the right spot is change one of the none/autodetect spots to the hard drive that you have installed (if it has been found once u press enter it should give you a list of options) and save and exit the bios.
Once you do this your computer should reboot and you should then be able to access the hard drive.
If you need any more help or need anything clarified because my instructions are a bit confusing then let me know.