That's untrue - 32bit Windows will only support a maximum of 3GB - the rest is reserved for graphics card mapping etc. In some cases, mine included, it only supports 2GB - it depends on the motherboard. I upgraded to Vista 64 to use all my RAM (having 6GB sitting idle is ridiculous!) I just bought an ipod touch, and as soon as I connected it it popped up a dialogue telling me I had to downgrade to XP or Vista 32. Screw that, I'm returning it now, so Apple can take the hit on it (since I've opened the package they can't re-sell it.)
Apple have always been worse than MS for trying to force people into using their hardware and software - the Windows version of itunes runs slow as hell compared to the Mac version - and believe me, my machine is faster than any Mac Apple currently sell (excluding the dual quad cores.)
Well, I was also going to buy a nice new imac for some relatives at xmas, but from now on, I'm not buying any more Apple kit.
And as for the Mac apologists/employees on here claiming "lots of software doesn't work" and it's all Microsoft's fault - garbage - I can plug most things in and they work fine - Vista 64 has been out for well over a year, I can play all my games, burn DVDs with no problems. In fact I can still play games from 5 years ago. There's no excuse for this, as Apple even have their own 64bit OS which (surprise surprise) does work with the ipod touch. Apple's obvious ploy here is to fool people into thinking it's Windows' fault and hoping people will buy a Mac out of ignorance.
I also own an iMac BTW, but it's a matter of principle. I want to use my PC which runs an operating system that Apple deem compatible.
I have Vista 64-Bit on my office computer because I need to test one of our products on 64-bit. However, I do not recommend it unless you really need it. As far as RAM, 64-Bit is only need if > 4gb since 32-bit supports up to 4GB.
I have had problems mostly with Drivers and some applications. The iPhone application may just be the first of many applications that you would like to use in the future that will not work. It really depends on how many 3rd party applications you want to use. Even Microsoft OneCare did not work on 64-Bit for a very long time. They recently released Version 2 "Beta" that finally supports 64-Bit. The reason they gave was that there just wasn't that many people on 64-Bit. Kind of a Catch-22.
However, it is more secure/reliable since it more of a closed system.
