Just a quick warning here,
DO NOT use Asus Update if you are using 64bit os, it will bork your bios, use EZFlash or AFUDOS
Re: Bios flashing
The old maxim 'If it aint broke don't fix it" has never been more pertinent.
Bios flashes should only be undertaken if you have a board problem or the new bios offers increased functionality.
The P5N has been known to have trouble with 2GB+ of memory at set up, you will need to check speed, timings and voltages in the bios to ensure it is running correctly.