I would say to upgrade your computer, but SWBG isn't a demanding game, so the problem eludes me. It might also be a problem due to to the low memory, as it could clog up the game along with the OS that's running. What is the native resolution of your video card, as you MIGHT be bottlenecking it, but that's a guess.
An Ubuntu user might be of more assistance, though.
"They are minor criminals! Marginal outlaws! You are inept!" ~ Darth Vader