Why would you want to downgrade your system? Vista is not a step forwards.
And why all the hype around 64-bit? It still has to run all your software in 32 bit. The type of CPU you have is a hybrid, not a true 64 bit CPU. It is only capable of 64-bit calls. The short answer is, the only thing 64-bit will give you is access to more RAM, and even this has been fixed for 32-bit. There could be a slight performance increase on the probably 2 x 64-bit apps out there, IE being one of them, but since programs like flash are not made for 64-bit, you'll still have to use the 32-bit version 98% of the time. There may actually be a performance decrease with 64-bit since 99.9% of your apps need to run in what is called 32 bit emulation mode (It is a 64-bit OS after all so you need to run your 32-bit programs in a sandbox, though many users may not notice this is happening outside of slightly decreased performance).
I could go on all day but the short answer is, 64-bit windows is still a novelty and one that might make your apps run slower since they need to be emulated. So, unless you want to run 20GB of RAM for some application (some vaporware application that you don't own yet) that you have, it is not worth it.
I've spoken my 2 cents.
-S
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