Micros POS-how do I know what ram to get

I have a friend who runs a few subway shops. They have a POS system with subway software pre-installed that was Purchased from Micros about 4 years ago. Currently 128MB of ram is installed and I have one open slot to add ram. THe system is Micros:Eclipse system unit. The numbers etched on the MB are 6011425 and MA973AE2440458 but no manufacturer logo anywhere. Win98 is installed. I want to upgrade the ram but dont know what kind it is or the max. No labels on the ram. How can I find this out. Micros charges to talk to someone and they want to do the job for an crazy amount of $$..