For me, I want Vista Ultimate 64 Bit to utilize the 8 gigs of RAM, because things will stop being made for XP soon and just for overall faster computing.
Well, first of all, you do need 64 bit, either XP or some version of Vista, to access your RAM. That's a given.
Second, "for overall faster computing", 32 bit is generally a bit faster or the same speed, and XP has consistently outperformed Vista in all gaming applications, sometimes by a little, sometimes by a lot. Even with driver optimizations closing the gap somewhat, there remains a real performance benefit to XP over Vista in gaming. There seems to be the general misconception that 64 bit is inherently faster than 32 bit. While it's true that 64 bit *chips*, e.g. C2D, Athlon 64 X2, etc. are faster than the older 32 bit chips, it's not because they are 64 bit. The move to 64 bit was made largely because of the need to address more memory in an efficient manner, which a 64 bit chip can do. (Basically a 32 bit chip can only access 2^32 bits of memory, it lacks the ability to distinguish between a larger number of separate bits natively). Benchmarks of the same hardware running 32 bit and 64 bit versions of an app show virtually no difference. One exception might be software that must compute things to a VERY high degree of precision, as a 64 bit OS and chip can do this natively, but we're talking about really rare apps, generally more precision than we can even come close to measuring in anything in the real world. (Such apps would most often be used in theoretical academic applications, quantum mechanical modelling, computational solutions in applied mathematics, etc.)
The biggest reason to go Vista right now is DX10 if you are a gamer. None of the games you listed are DX10 though. Even with DX10, it will be a long time before DX10 becomes a requirement for gaming.
As for what version of Vista to buy, don't waste your money on Vista Ultimate. There's virtually no difference between Ultimate and Home Premium, yet there's a big price difference. Unless you can articulate a reason to go with Ultimate, don't. Most people who have forked over the cash for it are resenting it because of the lack of advantages and the huge price tag. Ask yourself WHY exactly you want Ultimate, and make yourself list something it has that you care about before you spend the cash on it.
64 can go up to what, like 16 TB?
In theory, a true 64 bit chip could go up to 2^64 bits, or 18,446,744,073,709,551,616, or approximately 18 exabytes. That's a lot of space (an exabyte is 1024 petabytes, which is 1024 terabytes, which is 1024 gigabytes). The OS's are not written to handle this, and in fact, what we refer to as 64 bit chips are not fully 64 bit. The Athlon 64 uses a 40 bit (about 1 terabyte) physical memory addressing space and a 48 bit virtual memory addressing space (about 256 terabytes).
I guess they just figured there was no use at this point in time for addressing 18 exabytes of RAM. It gives you an idea though of how long it will be before we need to move from 64 bit chips to 128 bit chips for memory address space issues.
Another fun way to look at it is that if every human being on the planet (assuming 6 billion people) had 3.2gb of RAM, a single 64 bit chip has a sufficiently large memory addressing space to address all of this RAM at once (physical issues of connecting it all aside, of course).
32 bit can manage up to 3.5 with entries via registry 
