Windows 7 (and Vista) may not work so well on older hardware that's been running XP.
However, if you have the hardware to run Windows 7 and the software that works with it, then 64bit is little or no added effort over 32b.
The main value of 64b over 32b is in getting extra memory in some cases. Mainly, it makes up for the memory addresses lost when one uses a GPU with a lot of memory -- most are going to 1GB now, and that comes "off the top" with 32b -- its virtually free with 64b.
In the long run, as more applications are coded in 64b, there will be a definite speedup with well coded programs. Its not just extra memory. Working with 64b "chunks" gets more work done per CPU cycle for some machine instructions. Mostly, the speedup on well coded games will be in the 10 percent range (could be more or less). 10 percent is significant. For example, a lot of people pay a lot more for a GPU that gives 5 to 10 percent more. In the best cases, some test programs that just move stuff around ran almost twice as fast with 64b vs 32b on Linux (don't know how well that would work with Windows).
Anyhow, yeh, I agree with the above posts

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