I have a Dell Dimension 9100 that originally came with Windows XP Media Center 2005. I got rid of that, and installed x84 Vista. My frame rates are too low and I have a nvidia 7800 GTX. I remember getting 80+ fps with all settings maxed out. I want to revert back to XP 32 bit, which I have the CD of. However, every time I try to install XP, the setup fails because it could not find a hard drive. I then heard of slipstreaming. I'm having a hard time knowing which drivers to slip stream. Obviously, my hard drive drivers are needed, but I tried slipstreaming those and it did not work. What other drivers do I need in order for it to work? Are
IDE ATA/ATAPI controllers necessary drivers? How about my chipset drivers? I'm tired of wasting discs, so please somebody help me out. So I'm guessing I need to slipstream a crap load of drivers in order for XP to work. Should I find drivers for everything in my device manager?

If you still have your Dell installation CD that has all the drivers on it to get the installation going. Just put it in and boot from it the same way you installed Vista. You should also have another CD, a Drivers disk as well, or you can go to Dell's website to get the drivers. You don't need to slipstream anything.

Well I have no Dell Installation Disc, but how do I know the drivers match on the dell website with my computer. Do I have to slipstream all those drivers?

You do not need to slipstream anything.
If you do not have the original Dell CD, there should be an option in the BIOS somewhere for the SATA type, called "SATA Operation" down the left hand side. From the Dell service manual:



You'll want the second option. Or if that does fail, the Combination option.
Saving the changes will then mean the XP CD will see the hard drive.

With regards to the rest of the drivers, Dell's website has them. Just bash your Service Tag number in and everything you need is offered there.