I'm trying to update to Mountain Lion, currently running 10.6.8 as is required but the app store still says my machine is incompatible. I've run software update just to be sure, and I am up to date.
http://www.apple.com/osx/specs Your computer can't use Mountain Lion. Stay with 10.6 or buy Lion calling Apple
Here's a list of hardware requirements for Mountain Lion. It sounds like you don't meet them all.
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