Re: from a marketing perpective it doesn't seem to be such a great idea to overlap.
Could be. I don't think it would be a problem, though. A lot of people have 32-bit motherboards.
Intel doesn't seem to have a problem selling 2.2ghz P4's for almost twice as much as 2.2ghz celerons (same Intel "rating" and 64 being twice as much as 32 is a lot easier to explain to typical consumers than the difference between Pentium and Celeron.
I would expect the prices of all 32-bit processor to drop steadily over the next year, but that will hurt Intel, not AMD. Athlon-32 will replace Duron, and compete with the Hyperthreading 32-bit Pentium 4.
The 64-bit Athlons will be in class of their own, just like it was when the 386 competed with the 286.