I'd like to be able to play Portal 2 at the end of the month, and Skyrim at the end of the year at moderate settings..
720p, 2xAA, consistent 30fps is fine for me if that's all I can get.
When Skyrim comes out - I prefer to see everything at lower quality than fewer things at higher quality.
(so bigger draw distance with crummier textures, all the particle effects at lower quality, etc.)
Other then that you may want to grab you a 2GB more of DDR2 ram (given you are currently using 1-2GB on that system). You can score two 1gb sticks of DDR2 800mhz on ebay for about 20-25 bucks on average, sometimes cheaper.
Other then that not much else I can tell you. That alone will get you some performance gain for games with your current cpu, but like I said, cant comment on how well you will be able to run games that have not been released yet.
the general consensus among reviewers seems to be that the 5670 isn't as good as the 4770.. and if I can get the 4770 for the same price as the 5670.. seems like I should go with the 4770? Unless there's a bottleneck with my crummy processor that makes the difference moot..