I'm not sure if my computer is capable of running 64 bit at 4GB of RAM or not, haven't ever bothered to check because XP can't run anything greater than 2GB anyways. It's a 2.2ghz duo core processor--was top of the line when I purchased it 6 1/2 years ago--and it still runs fantastic. Now it's considered antiquated, not even 7 years later. That was after vista had come out and 7 was either just on the horizon or just barely out, so I specified tigerdirect.com to send me the latest with XP professional on it. I had hoped that windows would have learned to make an operating system in the past seven years, but I guess my hope was fallacious.
I know that there are extra spots in the tower for more ram, and of course, I could just put in larger chips. But it's all a little pointless--if I'm going to change OS entirely, then I would want to get a newer computer with a newer processor, because I still like XP, and I still have older games that I play in XP, such as Oblivion and Baldurs gate and even some old dos based games, like Bloodstone: An Epic Dwarven Tale (am I dating myself here?).
I know a few of those old games still have support for newer systems, but most of the ones on my pc don't. That may be why Wubi is the way to go, but it would still require some form of hardware upgrade. And an OS change.
Plus I may not be able to play any of the other new(er) games that I've had my eye on. Skyrim was the last one I looked at before I gave up hope. Then I saw PoE and I was like "whoah! Maybe there is a new game out there for me!" Unfortunately it sounds like it was just false advertising.