you need media center edition to stream video, you can stream pictures and audio with windows xp service pack 2 w/ the media connect plugin (free download for wga enabled machines). i think it only streams and doesn't actually allow you to store the files on the 360.
obviously wired is the best solution if possible. if its not possible, wireless will work.
i've only taken 1 guest on live with PDZ, i don't know if it supports 4 or not, but i personally like live because it lets me play with my friends while avoiding split screen.