Another technical thing to look for in multiplayer adventuregames is client/server side prediction. (IMHO it instantly becomes more like a RPG since you need to change concepts)
I did some tests with this using C++ and Blitz, and found out that instead of checking the players positions every game update isn't ideal: e.g do it one out of ten times. This way it doesnt consume bandwidth as much.
To avoid the lag because of this, I tried out using "cubic splines".
The idea is that you take the current player's position, and take the old player's position (one check before current one). Using this information PLUS the velocity (how fast/slow the changes are) you can use cubic splines to predict where the player WILL be, and adjust its coordinates every cycle.
Find all about it here, I'm not very good at explaining things often
http://www.gamedev.net/reference/programming/features/cubicsplines/page2.asp
