P4M890 is still the same UniChrome Pro DX7 IGP found on K8M800 and P4M800. Only the P4M900 has the new Chrome9 HC DX9 IGP, also found on K8M890.
I mentioned some months ago on VIA Forums how prone to confusion this inconsistent naming scheme would be. I could see people easily [and reasonably] assuming that P4M890 is the Intel version of K8M890, but alas...
To summarize:
P4M800 = old UniChrome Pro (DX7)
P4M890 = old UniChrome Pro (DX7)
K8M890 = new Chrome9 HC (DX9)
P4M900 = new Chrome9 HC (DX9)
Can I play HL-2/DOOM3 on the least possible configuration or not.
I would say "not" with reasonable confidence. You *might* be able to get playable frame rates with a higher-end processor and plenty of RAM by reducing graphic detail to the lowest possible. Otherwise, probably not.