I have an old asus P4P800 deluxe motherboard. I installed 1 gig (2 512 sticks) of corsair. I bought two sticks of Patriot 1gig pc-3200 400mhz to upgrade the memory.
They failed to post and when I reinstalled the old memory they too failed at first but on a second try by immediately pressing the delete key I was able to get into the setup. I just indicated to continue without changing a thing, and things proceeded normally and all was fine.
I was informed on several websites that this patriot memory was compatible, but I guess not unless someone has an idea to get them to work.