If you like the new graphical interface of Windows Vista, but prefer to continue with the friendliness of your XP, Transform XP to Vista is a good solution to get you going.
It's a simple package containing a desktop with the look of Vista and many of the applications you'll find in Vista Start Menu and Yahoo! Widgets. It's easy to install, you can choose the three main components of the package or any of them, and if you get tired of Transform XP to Vista, you can uninstall it with equal ease. The package also includes Yahoo widgets which is basically a collection of small and useful desktop assistants. This includes anything from a PC temperature gauge to mini games. The Vista Start Menu is modified not only in appearance but also in functionality. You'll find a few new tools on there that aren't in XP and it's basically a lot more accessible although some things, like "Communication Centre" have been renamed.
A cool little package that will save you a packet on Vista's hefty price tag but won't leave you with all the compatibility problems associated with it.