I have a late 06 20" iMac with 2.16 GHz C2D. I have 4 GB of ram in it, but I seem to recall that the Intel chipset or something was not able to make more than 3 GB or something actually available to the system. Is this true? If so, that sucks, because I hear that the main speed improvements in using 64-bit Windows over 32-bit come when you have 4GB ram. I just installed Windows 7 RC 64-bit in hopes of it making my CAD work go a little smoother/faster, which is what other CAD people say it indeed does, at least if you have 4GB ram.