Let me start by saying you'll need an iPhone/iPod Touch to use this because it's an app. And for right now it'll work over WiFi networks only, so creating an ad-hoc network is necessary if your phone/ipod isn't hooked up to the same wireless network.
I'm sure some of you have heard of Air Mouse, but there's a FREE alternative that Logitech puts out called 'TouchMouse.' It's great!! Install the app on your phone and also your computer and say hello to two-finger scrolling!
Mess around with the settings and trust me you'll love it. Keep in mind this version is only '1.0' but it still works great. It works with Win XP/Vista/7 (both 32/64bit) and also OSX. Give it a try.