You may consider a finding used 2600XT over the 3850 simply becasuse your processor will probably prevent the 3850 from giving you a performance increase over what the 2600XT will give you. Personally I wouldn't waste a lot of money on an AGP system but Newegg has the 3850 AGP for a $99- $120. I also would avoid the Powercolor card due to potential problems.
I am happy for both of you. My experience was much different albeit, with only one model, the 4870 1gb PCS+! After 3 seperate premium priced cards and how they changed design and then downgraded its clocks after reviews, I feel Powercolor has problems.
Powercolor is fine. As peaks said 3850 is the best you can get in agp, but there outrageously expensive. You can get a HD4850 pci-e for $10 more than the HD3850 agp.
PowerColor makes a decent card, although they have the fan run at 100% on some models like my PCIe HD 3850. Since all you are doing is playing back HD video, both the 2600 XT and the HD 3850 have a roughly similar onboard video decoder (UVD/UVD+) and support HDMI + audio. I would go with the less-expensive 2600 XT in that case.