Nothing wrong with Vista x64 other than your perception. Windows 7 will be an improvement upon Vista. If you want 64-bit, I would avoid Windows XP. If you want 32-bit, then by all means, have at it. Though why people continue to cling to XP at this point puzzles me. Makes absolutely no sense to build a new computer with the choicest new components and then stick a 7+ year-old OS on it.
If this was 2 years ago, I'd understand it a bit more. However, all of the reasons people thought they needed to avoid Vista are gone. Vista performs on par with XP on the same hardware. It isn't the "memory hog" that people have claimed; that was a misconception right from the start. Also, SP 2 is imminent, which may or may not give users further improvement... but it will certainly help with any bugs that might still be present.
In short, Vista is not, nor has it ever been, like ME. The comparison is ridiculous. If you still want to avoid though and still want 64-bit, then you'll have to wait for Win 7 or go with Linux. Win XP x64 was a stop-gap solution at best... and MS didn't put much effort into getting vendors to support it.