Roshi, the WinXP-64 beta is free. (And that's a good thing, since it's currently a hunk of junk as there are no real drivers, and application support is scarce.)
As for ME, there's a reason everyone (even MS lovers) hate Win-ME: it just sux! It's generally agreed that it was the least compatable, worst made, most buggy OS Microsoft put out.
WinME is a waste of your money and you probably can't even find a copy of it anymore. As for WinXP-64, I wouldn't touch a beta OS if my life depended on it and I had a ten foot pole.