I'm buying a new monitor with a resolution of 2560x1440. Will my existing graphics card, an Nvidia 7900GS, support this resolution for 2D work?
It should. The max resolution of the 7900GS is 2560 x 1600. You need to be sure that you are using a dual-link DVI cable, as the maximum resolution supported by single-link DVI is 1920x1200.