Only a couple of games like BF2 use more than 1 gig.
The other thing is the command rate of your memory would most likely switch to the slower 2T settings.
You can give it a try, and then run some benchmarks and see how much difference there is. It's good experience.
I did this for my X850XTPE computer, it ran better & faster with 1x512mb stick at 1T than 2x512mb at 2T. I'm looking to get a 1gig stick for it now.
BTW it's a SIS chipset.