PCI express is supposed to start showing up late this summer or fall. As for it and 64bit computing going "mainstream", well, that depends on what you mean by mainstream. If by mainstream you mean 50% or more of home users have it, then that's probably a good 18 months to 2 years away at the rate most people update their machine. Remember, most people aren't gamers who always want the fastest thing just because it's the fastest thing. Most people want the cheapest thing, because it's the cheapest thing.
I really don't see why you need it to go mainstream anyway. I'd just wait until PCI express is out and you can get a decent video card to go with it. Remember, PCI express is meant to replace AGP, so your PCI express board probably won't have an AGP slot for your existing video card.
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