It looks like you’re replacing a low end nVidia card with a low end ATI card. I assume by “gaming computer” you’ll want to play the latest and greatest, as well as the latest for the next 2+ years. If you’re only really interested in older games, that system would be more than adequate.
But when it comes to gaming computers, the video card is the single most important component, and you won’t be too happy with your performance with $80 video cards, generally. You don’t have to spend $400, though - something along the lines of $150 is usually pretty decent.
Looking up test graphs, it appears the 6600 GT beats it cleanly in most directx 9 tests - which was a midrange card in like 2004. I’m not sure if it beats the 7300 LE you were considering before, as that card wasn’t a part of those tests. But they’re probably within the same range.
You would be much happier just spending 1100 instead, and getting a decent mid-range video card (or even downgrading the processor and memory to get a better video card and stay under 1000).
You can get a geforce 7600GS for around $120 (strangely the 7800 GT seems to be being phased out, or something… at least there are no new ones on newegg. I was going to recommend that for price/performane), a 7900GS for $170 (there are a few listed in the $140s), or $110 for a X1600 Pro.
The geforces would run circles around the X1300. I’m not too familiar with the ATI product line anymore, and they have confusing nomenclature, but I’m guessing the X1600 would too.
The naming system for video cards can be a little confusing. For instance x1300 doesn’t mean it’s better than an X800 - it’s actually probably a significant downgrade - it just means it’s from the next generation. And all that XT, XTX, PRO, etc stuff can get confusing.
With Geforces “LE” usually means a cheap, stripped down version, “GT” typically means more pipelines than the unlettered versions of a card, GS is a lower cost but roughly equivelant performance version of the GTs IIRC, not sure what the internal differences are.
But like I said, I wouldn’t try to skimp on your video card to keep the total cost down. It’d be better to have a $1150 system that flies than a $1000 system that struggles with games because you wanted to save some money on what is the most important component on a gaming rig.