To hold you until you get some more RAM, you should disable/exit any programs you may be running in tandem with your game. That includes anti-virus software, IM programs, etc.
Having only 140 mb available for a game is not really a good idea, especially for XP. BTW, what programs do you have running. I use about 120 mb and that's running Mozilla, Trillian, my video card tweaker, Daemon Tools and the NVIDIA nForce audio control panel.