You can't always just "buy" something to see if it fixes the problem. If you have friends who have computers, see if they will let you borrow their ram for an hour or so, assuming it's the correct SDRAM. Make note of the speed of those modules, too.
Have you tried using each stick on it's own independently? Put one of your 128-mb sticks in and see if your problem continues. If it does, try the other stick on its own. If either of them seems to be causing the problem, try and replace it if you have memory/$$$ available. When you do this, try both (or all) of your memory slots on your motherboard.
Good luck! Let us know the results of anything you do.
You're the guy from that hamburger train, right?