I am really sorry you are having so many problems with ASUS mother boards. I use a lot of ASUS products and two mother boards are part of them.
You say the memory posts incorrectly? What do you mean? The memory will show a loss for onboard sound and video.
Are you using onboard video? Also, Windows takes a portion of your memory as well. For example, I have 2 GB Ram but only 1.4 available.
ASUS makes some great stuff but they are bad explaining it. They also will let you update your BIOS using there "flash" system but they do not warn you that it won't work with your mother board.
You downloaded the wrong BIOS. I know because you have an 800FSB and the BIOS you downloaded has a 533FSB.
That's ok. You need to download the right one. Wait!
Something I want you to know. ASUS downloads must be done individually. One at time.
That means you download the update and you restart the computer for every one!
Believe me when I say this! I have an ASUS P4C800-E and had to wipe my computer three times due to my impatience.
Oh and lastly, don't believe everything ASUS says. If your computer is working good don't fix it.
There is much more I can tell you about ASUS but this post is getting long.
Let me know,
Your Hardware Guide.