What I would do I were you is download Ubuntu, burn it, boot it up from CD and see if you can get the essentials working (network/internet/GUI). After that you could procede to install it if you like it.
I would stay away from the x64 version at the moment. It will be more trouble then that is is worth for a consumer atm. You will have trouble with Flash, wmv, realplayer and other non-open stuff.
VLC player or Mplayer can handle all your Xvid/divX needs.
Good luck and have fun
Everything is possible, some things will just take more trouble to set up then others.