In my opinion, what ultimately determines if Vista can run with the Aero special features, is not the amount of memory -- its the graphics chip, its strength. It is a well-known fact that a graphics card with a certain chipset delivers virtually no increased performance with a higher amount of VRAM, especially on low-memory tasks.
Microsoft, like any other software developers, just chooses to put a minimum amount of VRAM as a system requirement for Vista. But thats probably because there is no ratings system for graphics chips. I mean, can you immediately judge if a GeForce 6600 is faster than a GeForce 5900? And how do these chipsets compare to an ATI graphics card? The only statistic on a graphics card that will give the general user a rough indication of the cards power, is memory amount, because memory amount has over the years been on par with increasing chipset power.
So when judging whether Vista will run on current Intel Macs, look at the chipset, not only the memory. According to Dell, to enjoy Aero, you computer should have: at least 1 GB of RAM, a DVD drive, a fast hard drive, a dual-core processor, and non-integrated graphics. However, for Vista without the new GUI, you just need 512 megs of RAM and a modern processor. Which means all Intel Macs should be fine.
