The 128mb will get you medium to high settings on most modern games. Although some like BF2, or Quake 4 you may have to tone it down slightly. Other games like Call of Duty 2 will play at full everything as long as you have at least 1GB memory.
Now thats today. In 3 months and 6 months as the next generation of games come out, you will probably see a need for lowering graphics to medium levels. And in a year or two you will be playing closer to the lower levels.
The 128mb might last you up to three years playing modern high graphics games, but by the end of it, you will start to experience low frame rates even at the lowest levels.
So, if you want to play modern games at good frames per second through college, get the 256. Or if you are like me, you will get the 128, and enjoy the modern games while you can, and in a year or two, once you arnt top of the line, you will go back to playing starcraft. It never gets old.
I would say if you are not a hardcore gamer, you may regret not getting the 256, but you could save your money for things more important to you, because if you really were a gamer, you wouldn'y be getting a laptop anyways.