PC graphics upgrading help?

We bought a computer about 9 months ago(I was still a noob in PC hardware back then). It has 2.66ghz core 2 duo, 3gb DDR2 of RAM, 250gb hard drive and a geforce 9500gt. A few months after we bought it, i just realized that i should have invested in a better graphics card. So Christmas my brother and are planning to buy a better one and a new hard drive. Can't decide whether I'm gonna buy a 9800GT or a GTS 250(These are the only ones we can afford right now). Since our PC ain't that good, we're gonna buy a new one about 2 years from now. What would you recommend? Would the 9800 be obsolete in 2 years time? Will it play games on Medium high to high settings in 2 years? Or should I go with the GTS250?