That's what i've been trying to say.
Mainstream doesn't necessarily mean high percentage of ownership. It's the price that makes it fit into the mainstream bracket. At a price bracket of around ~$140, the 7900gs is a killer deal, especially when you weigh them against slower performers that cost ridiculous amounts on an agp system, or the lesser performing 7600gt/x1650's.
But anyways, the bottom line is that:
Don't buy that card. Save some money, and you won't regret it in the long run when you're faced with the hole in your pocket that you had spent on a card that would be rotting away in your old old AGP based system.
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AMD X2 3600+@3.00|2GB Crucial Ballistix Tracer PC2-8500|evga 7900 gs (750/1780) Volt-moded|ASUS M2N32-SLI Deluxe|2 x NEC Multisync 90GX2 19"