DDR does not work in DDR2 mobos, however currently all Athlon cpus/motherboards are DDR only. Note that when DDR2 Athlon motherboards and cpus come out, they won't work with DDR Athlon cpus and motherboard. IMO, the Athlon X2 Dual core is better than the Athlon 64 FX, the FX runs at a faster speed, but the X2 has two cpus. For multitasking and general desktop use the X2 will perform better, and will probably perform better once games are optimized for dual core.
32 bit applications do work in Windows 64 bit, however not all hardware has 64 bit drivers so far. Also, with an Athlon 64 you can still use 32 bit Windows, so you're not forced to upgrade. I haven't heard any concrete advantages to 64 bit Windows (some people say it runs smoother, but that may not be real), so you're probably better off waiting until Vista to go 64 bit.
BTW, I would have liked to see an Athlon XP on those tests....wondering how my Athlon XP with a 221mhz fsb would compare. It's got memory latency about 20% lower than a normal Athlon XP 3200+ system, so maybe it could compare to a 3ghz P4? I don't really have any good programs to use to compare, but in synthetic tests (memory bandwidth, latency, etc) it performs about as well as a 3ghz P4, and the P4s usually perform better in synthetic tests than actual games.
