TightVNC works really well for this. I am in the process of moving my MJ8 server into the garage at which point I will only have VNC access to it. Even over 802.11b it's usable - make sure you choose TightVNC encoding, the last version I installed did not default to the tightvnc encoding [odd eh?]. Also you will want to configure the server to run in "full poll mode" - or you may end up with odd artifacts (non updating fields etc) - typical of VNC interaction. When I need to rip a new CD I pop it into MJ8 server and rip it from a nearby computer when I remember to / have the urge. I buy about 2 CDs a month at this point (and I always buy the music I want to have on demand access to).
I am very interseted in another way to control MJ remotely - especially so that I can store the MJ8 server and storage and audio card, somewhere else (garage). I don't want another device in my media room - my Tivo is loud and annoying enough, no need to add another "quiet" PC. Frankly once I've got a DVI in display - the DVD player is sold and the Tivo is a museum piece. I'll have nothing but a display, pre-amp, amp, speakers, sub and a wireless keyboard (surf, shop, shop, surf, order dinner...) in my theatre room.