It will suffice for now and for probably a year or so. You can run almost any game with high detail settings and resolution with it as far as I'm aware.
If I were you I would probably hold off a little and look at saving a little extra. The 7800GT is still very expensive and overkill for the majority of users.
Shop around, you won't be disappointed with the 6600GT I'm sure, but as it's not at the cutting edge now it won't have the lifespan of the latest cards. I've just purchased a 6800GT for use in my new system, with the hope of adding a second in SLI sometime in the future. That could be an option for you, though it depends on if your current motherboard supports it.
Have a look around at benchmarks on the net and see if you think it performs well enough with todays games to handle those in future years. If not, hold off and save a little more.
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