Your hardware can support a 64 bit operating system. There is no price difference between the two versions, so I would recommend the 64 bit OS. If you wanted to use more than ~3.25GB of RAM, you can with the 64 bit, but not the 32 bit OS.
Your Mobo & CPU will definitely a good to go for X64 edition of windows 7.
32 bit windows won't support more than 3 GB ram.
64 bit is the Present & Near future (Soon 128 bit may come), 32 bit OS is a kinda obsolete now.
For supporting & to keep alive the existing 32bit systems only the 32 bit versions of Windows 7 is out.
I afraid that same thing will happen with next version of windows. (Doubtful about 32bit Support)
I strongly recommend you to go to Windows 7 64 bit only.
As aford said there is no price difference. You can blindly choose 64bit Windows 7.
64 bit is the Present & Near future (Soon 128 bit may come)
Nope. If you're talking about using 128-bit data, then that's old hat. Intel x32 and x64 CPUs have included 128-bit data registers ever since SSE was announced in 1999.
If you're talking about using 128-bit addressing, it ain't happening any time soon. Let me paint you a picture: think of the 4GB of RAM memory that's addressable using a 32-bit address as if it was a single sheet of paper. My computer has 12GB of memory - that's like 3 sheets of paper.
Here's the rub - going from 32-bit to 64-bit addressing multiplies the amount of accessible memory by 4 billion times. So the memory accessible by a 64-bit computer is equivalent to a stack of 4 billion sheets of paper - that would be well over 600 MILES high.
Big computers today may use the equivalent of "several" to "dozens" of sheets of paper. The Server versions of Windows top out at 2TB, equivalent to a 20-inch stack of paper. Do you really think there's going to be a need for "600 miles" of memory any time in the next couple of decades?