also, check the IDE cable. I had a bad cable that did this that had a bad ground/signal wire that vibration caused it to open causing issues. Including data corruption and frequent stalls in OS X.

So try replacing the drive, but I would back up your data using a different disc as the install disc, then if you can run a program like Norton, look for bad blocks. If you see any/get stalls, chances are the drive is bad. Replace and retest.