Are you talking about memory or disk space? "246MB" is your free disk space, which isn't alot.
If you are getting a memory error message, it is probably refering to the amount of RAM in your computer (16mb, 32mb, 64mb, etc..)
I would try starting a game with nothing else running except your browser. This includes programs running in the background and programs running in your taskbar (like a virus protection program, ICQ, AOL IM, etc).
If you hit CTRL-ALT-DEL at the same time, you can see exactly what is running.