AMD is in no way responsible for posting system requirements on their boxes, they do not sell their cards anymore, all cards are sold via OEM so you lose on that count, you should be suing the OEM you bought it from instead but its not their chip on the card causing the issue so they arent really liable for the issue. Also their card is compatible, you can see your desktop with it right? If you can see your desktop then it is compatible and functional, game perfomance issues are caused by the combination of many seperate drivers that may or may not play nicely within the operating system
Also a 3850 is a high end card, it was one of the best cards available a while ago, but then the G200 and 4xxx series came out but the 3850 is still a high end card relative to most out there.
And i also googled the 2 things that you said to in your post, only a little over 7000 hits, if i was AMD i would be very proud of that number, probably a million cards sold between the 3850 and the 2600 and only 7000 issues is damn good.
Quit being whiny and dont expect modern tech to work well with an old system without a fair amount of tinkering, if you want it to just work, get a mac but never plan to upgrade, but even they dont always work, it is impossible to make software or hardware work on all possible systems, i would never have even considered putting a 3850 onto my old pentium 4 even though it had an AGP slot.
In the future, do research, ask questions, and fix the issue, and if it cant be fixed return the hardware as faulty. Dont bitch everywhere you can, it just proves that the problem isnt in the computer, its in the chair.