Am I missing out on anything by sticking by Windows XP?
XP 64-bit isn't very "polished", with a lot of missing drivers, and a 64-bit OS is the only reasonable way to get more than 4Gb of addressable RAM.
Try out the Windows 7 RC (while you can), it doesn't really matter if your computer is old.
Tom's Hardware reported they got it working on a Pentium II. I got it working on a 6-7 year old laptop with a P4 processor and 512 MB ram. Only had a problem with my network card drivers, which I had no idea where to get compatible ones, but the rest worked straight "out of the box".
If you have a spare hard drive or your current one is large enough (+20 gb to be safe), just create a dual boot and give it a try! You will find out if drivers are an issue and if it runs smoothly.
In general I found Windows 7 a nice improvement over Windows XP, if only it were for the UI, so just give it a try, that's what the RC is for!
I though that too, and there was a campaign in the media saying Vista was a nightmare.
The truth is I found it very easy to use. Granted I got it from a new computer. I guess the problem was the upgrade from existing XP installation.
It runs fine. I do that too on XP, bu in Vista there was no need. It all in the new hardware you buy.
If you have the money, go on, upgrade, or even better: Switch to mac