A single gig of RAM for such a huge site . If you are sure the reason for crashing is not a hardware failure or such, the first thing I would do is to add more RAM. Configure MySQL to hold all indexes into RAM to relieve hd load.
Actually I just looked at the task manager to check, it's barely using half the RAM. That has never seemed an issue to me. If I go the route of tossing all indices into RAM, would that really take up the other 500mb?