Thank guys for your ideas. I solved the problem.
First I found an article on AMD forums:http://wwwpub.amd.com/products/cpg/athlon-duron/amd_win2k_patch.html
Description of Issue
An issue has been identified that could result in the corruption of video data shared between AGP graphics adapters and AMD Athlon™ or AMD Duron™ processors, including the AMD Athlon™ MP processor when running Microsoft Windows®2000 Professional, Windows®2000 Server, or Windows®2000 Advanced Server. This issue is independent of system chipset and has been observed when running Ziff-Davis 3D Winbench™ 2000 and Mad Onion 3DMark™ 2000 in benchmarking mode.
AMD and Microsoft have worked together to identify a patch that involves adding a key to the registry. To add the key run the registry key installation file below or add the registry key as detailed in Microsoft KnowledgeBase article Q270715. AMD recommends that AMD Athlon™ and AMD Duron™ processor, including AMD Athlon™ MP processor users with AGP graphics adapters running Microsoft Windows®2000 Professional, Windows®2000 Server, or Windows®2000 Advanced Server install this patch.
Although they say it's for Win 2000 I tried it anyway and it worked. My score in 3D Mark are like 1000 points higer from problem state and about 200 points higher from previous slower CPU.
Next I found and installed update for 3D Mark. Now it correctly identifies my CPU.