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In short - May to late summer for PCI express. The prototypes are circulating now.
Video cards will be same time frame. ATI has an "integrated" solution Nvidia uses a "translator chip". Both will work fine for the bottom end "PCI Express" speeds for video to MB speeds.
Don't worry about vid card speed. PCI express bottom end is much faster than AGP and AGP speed over 4X is barely used. AGP 8X benchmarks about the same as AGP 4X.
There will be no real system speed improvements this year. PCI express is faster than you need in a PC. The advantage will come with really high speed HD's, maybe optical and multiple USB 2.0 and Firewire devices.
So I guess there is no point in upgrading my PC before the end of the year or maybe Q1, 2005. I am looking forward to upgrading it though, as I tend to get invited to Beta Test Microsoft Operating Systems and I want to be at the cutting edge (Bleeding edge?) of technology.