RAM upgrade is no enough to run ML.
Other components such as PSU, logic board and graphocs are also important.
So if you are not on the list here:
you will waste your money on ML.
It's mainly the video card. The Models 2,1 through 4,1 have video cards with non-upgradeable 32bit drivers. The model 5,1 Late 2008 and newer have at least the NVIDIA GeForce 9400M with 64bit drivers. Mountain Lion requires 64bit native drivers. Mountain Lion no longer supports Intel's GMA 950 or GMA X3100 graphics processors.
While Lion used some 32 bit and a lot of 64 bit code, Mountain Lion is pure 64 bit, which excludes more systems than Lion did. It's not something you can add memory to, for example, as it involves the base architecture.