You will probably recieve an error when downloading the client update that informs you that your video card driver will have problems with the game.
No worries. An employee of Nvidia was telling people that Nvidia is releasing a new driver that will solve this problem before the release of GW2. If you want to solve this problem before the stress test, you can download the last Nvidia beta driver.
The good news: you're going to get anywhere between a 10 - 70 percent performance increase with the new driver.
Anyways, if you have any questions, post them here. There is a thread discussing this in the Guru forums in the Tyrian assembly forum. If you scroll back you should find it. If not, I can dig it up for you, but probably won't be available to help you find it until after today's stress test.