I've been running ubuntu since heron came out in april and there's a fairly stiff learning curve involved with it. Compiz fusion is very pretty but a little resource hungry.
Download Ubuntu here
Ubuntu 8.04.1 LTS (Hardy Heron)
You can also dualboot windows and Ubuntu if you like
Ubuntu:Hardy -
Compiz Fusion instructions are here.
How to install Compiz Fusion in Ubuntu Hardy Heron. « Future isn’t around the corner, it’s here!
Overall I'm really enjoying it and I'm tempted to change my wife's computer over to it as well. I built a linuxMCE computer yesterday for shits and grins I'm going to eventually runa linux media computer in my living room.