Just built a new system with Vista64, and it was painless, and runs like greased lightning.
It is NOT a resource hog, unless you have every bit of Vista eye-candy turned on, and even then, with the x64 version you can easily supply it far more memory than you could in XP due to the 4GB limit. Secondly, since it tries to preload your most commonly used applications and documents in memory, it might appear to start up slower and use more RAM than it 'should', but it is actually saving you time by putting your stuff into RAM before you ask for it. This feature can be turned off. Thirdly, it is very cheap to put 6GB on the newer motherboards that have the slots and the capability to address that ram from the BIOS. Since by default, WinXP takes half your available RAM for system use, and the absolute max RAM under XP x32 is 4GB, then XP is taking up to 2GB of your RAM. Since part of the 4GB limit is used up by video card RAM, which has to be addressed out of the 4GB pool, your apps will probably never even see more than 1.8GB available to them, and with a browser open and a security suite, etc., running in the background, it is more common to have no more than a full GB effectively available to a single app! After using Vista x64 with 6GB of RAM for two months, I have never seen it take as much RAM for itself as my 4GB XP system used to take. So the 'resource hog' label is completely inaccurate, at least in comparing anything like apples to apples with XP. Of course, don't turn on live video wallpaper and Aero graphics that allow translucent window frames, etc. (But you can see the motion graphics of the wallpaper through the translucent frames!) That is obviously going to take more resources than plain XP. Duh.
Upgrading a three or four-year-old system, for example, to Vista x64 might not be the best idea, however. You would want to verify that your existing hardware is compatible. For a painless upgrade, using hardware that is certified Vista-ready is the ideal.
Ultimately, the really BIG reason to go to Vista x64 right now is to be able to put 6 to 12 GB of RAM to use in an app like PS. In some apps, you can also get improvements from 64-bit computing, but most apps just haven't been written to benefit from that yet, so RAM is still the prime reason. There IS a difference between a Vista x64-compatible app, and a 64-bit app. Some 32-bit apps have been re-compiled to be 'compatible' with Vista64. You effectively get no real gains, even in memory utilization. Some apps have been tweaked to at least use some degree of additional memory under a 64-bit OS, but again, they still aren't really true '64-bit apps' under the hood. Finally, there are a small number of apps that are written to truly be optimized for a 64-bit system. The number of these applications are still relatively small. And then there is the extra complication of all the support drivers, such as the Wacom driver, the 3DConnexion driver for a 3D mouse (and the PS plugin for the 3D mouse), etc. Right now, the standard Inuos3 pen works fine in CS4 x64, but I can't get rotation to work with the 6D Art pen within CS4 on my Vista64 system. Also, the 3DConnexion Space Traveller 3D mouse works under Vista64, but the CS4 plugin that enables the 3D mouse within CS4 apparently only works in conjunction with CS4 x32, not CS4 x64. (A version of CS4 is installed in both the Program Files directory and the Program Files x86 directory. The x86 directory is where 32-bit programs are installed under Vista64.)
There is a Settings and File backup utility built into XP: Go to Start->Programs->Accessories->System Tools->Files and Settings Transfer Wizard. This will backup and compress all files and settings, BUT I don't know how well this works when you are going from XP to Vista. It might be safer overall to just install Vista on a new primary harddrive, and keep your old XP drive unchanged for the next 6 months or so, so that you can always go back to it to hunt down some files that you completely forgot about, such as those custom brush files or the custom filters or actions you bought online and installed in a unique location.
"Talent and all that for the most part is nothing but hogwash. Any schoolboy with a little aptitude might very well draw better than I perhaps; but what he most often lacks is the tough yearning for realization, the teeth-grinding obstinacy and saying: even though I know I'm not capable of it, I'm still going to do it." -- M.C. Escher, in a letter to his son Arthur, 12 February 1955