BIOS = Basic Input / Output System - Chip/File that contains the instructions for how your system should boot and how your system operates. Also the BIOS Chip/File contains Instructions for the computer's POST as well as Containing the CMOS Setup
About Updating/Flashing the BIOS yes you should if you use "Top-Of-The-Line" hardware, but should not need to Frequently.
You can find out if you need to Update/Flash it by going to the Manufactures Website 95% of the time. WARNING FLASHING YOUR BIOS CAN BE VERY UNHEALTHY IF YOU FLASH WITH WRONG ONE!
POST = Power On Self Test - Test a computer does to see if the necessary hardware is present/functioning.
CMOS Setup = Complementary Metal Oxide Semiconductor Setup - Config program that allows you to configure hardware settings including system settings such as computer passwords, time, and date. Then stores on CMOS Chip.
Hope this Helps!
Edited by LoLucky, 23 February 2005 - 01:41 PM.