I am lucky enough to own a rather high end custom built PC.
I have found that not only with this game but with other games as well that it is a good idea to stick with the games recommendations as far as the graphics and effects.
It tends to lower the chances of crashing due to incompatible settings.
And just that is completely wrong! You don't need AA in a reealistic-graphics-game in HD. But in Borderlands, there are all the thick black lines that should look like painted - but they don't due to the lack of Anti Aliasing! I don't need AA in Bioshock or UT3 or Crysis, but Borderlands looks a thousand ways better with AA.