Update: Please check out my other entry involving poor speed in general with iTunes 7 and Vista.
Running with the default Vista installation, you get a feature called User Account Control, which basically lets you be an Administrator on the machine (like you were by default in XP), but every program you run will run in the context of a normal user, in order to prevent programs from having too much access to parts of the operating system, say, a virus or spyware.
It seemed to work okay, only running into a problem with a few programs. There's an option for programs that won't behave that can force the program to run as an administrator, and that usually takes care of the problem. iTunes, though, complains that it's in "compatability mode". Also, every now and then inside of iTunes, it will pop up an error saying that it could not write to the iTunes library. This causes you to lose any new files you just added, etc.-- major bummer.
Searching Google for iTunes and Vista doesn't really yield any valuable results, and I have to run iTunes.. just no way around it for my iPod.. so I had to disable UAC. I probably was going to disable it anyway, being a "advanced user", but for typical PC users, I can see UAC being a great tool in preventing bad software from affecting your operating system.
Anyway, hopefully this blog entry is helpful to anyone else who stumbles on this problem, and hopefully Apple's next version of iTunes takes care of the problems..