Apple is making the most of use of GPUs from the bundled software, OS integrated perspective. At $799 a Mac mini is a decent start towards an amateur editing station though I would honestly recommend stepping up to an iMac, especially if you want to see the HD as you're editing HD.
iMovie (part of the iLife bundle) supports HD and while they're newer user interface isn't as cool (IMHO) as the older UI, it's a great editing application for beginners. PM if you need any more help.
Have fun!