Ok, I didn't completely understand your problem.
So you have One or Two hard drives in your computer? It sounded to me like you have two, and when you try installing things to your secondary (slave) drive, or saving files to it, your computer laggs up.
Xp/Vista? How long have you had this computer? I'm assuming it's not your video card. If it has a 3.2ghz processor it's pobably fairly new, and even if it was old it could handle a DVD unless your vid. card was frying.
Here are some hdd tests. Choose the one for your harddrive and run it.