Literally just test the drive with seatools. It will tell you if it's going bad or not at that's that. The fact that you're using a very old tech, with something current is also bound to cause a whole range of issues including like what I said before, a more noticeable lag time.
You can keep asking why it would be the hard drive and all of us are giving you reasons why.
Also, you need to get matching ram, or you're going to run into even more issues there.
Get these, nice speed and cheap.
And for a new HDD get this one.
http://www.newegg.com/Product/Produc...82E16822148395Edited by metroidfreak - 2/21/11 at 1:04pm