You arn't switching drives, you are ADDING your laptop drive.

Your desktop has a harddisk controller that allows two devices per IDE cable chain. When you open your desktop up, you will see a flat long cable running from the mother board to the dekstop's hard drive. On this long, flat cable should be another free molex connector. This allows you to run two drives on the same chain.

After you install your laptops drive (by plugging it into the IDE chain cable and a molex cable that supplies power), your computer will now have two drives. If you tried to start up at this point, your dekstop would be very confused as to which drive it should "boot from". It wouldn't know whether to run Windows from your desktop or laptop drive.

And thats why you need to set one as a slave and one as a master. Their should be a little jumper chart on the back of each drive, and a little set of pins with a connecter that allows you to cross two adjacent pins. You need to set your desktop's hard drive to master, and your old laptop drive as a slave. That way, when you start up, the computer will check the hard drives, identify the "master" drive, and use the boot record and Windows installation from that drive to start up. Then, once Windows is booted, your slave drive will now be available in your "My Computer" under a new drive name like "D:" or "F:".

Now you can access all the files on your laptop drive from Windows, without needing to actually run Windows from it. All your old Windows files and folders will be sitting on the drive twidling their thumbs while you snatch all the good files off.

Hope that is enough to get you started. It should become fairly self explanatory when you check the jumpers on the drives and see the cable arrangement.

Cassidy