ehhm, Babrook.
There is one thing with those games .
They arent MMO or if they are they arent at alpha stage whith an update system, where you cant be really sure if all players have the same.
And yes it works with 256 MB RAM,
It works on following setting pretty lag-less:
ADSL,
128 MB Graphics card (GeForce 5200),
1 GHz AMD,
one GB or so free disk space,