I think your computer should work fine with 4 ram sticks, but I don't think you can o/c as high on the upper end. I would think 400FSB should be fine. There was a problem with Windows XP which couldn't handle 4GB or ram and would recognize only 3.2G or whatever. Vista solved that problem.

When you RMA an item, usually you have to contact the RMA dept and get an RMA number. Then you send them the item... then they either fix it, or send you back a new one.