Nearly all computers manufactured today have motherboards which use bios chips based on flash memory technology
threw your motherboards bios which can be accessed at startup
Motherboards are a big collection of chips and wires. I recommend that you go to Google Images and see a lot of examples of motherboards.
Two examples are resetting the BIOS to the default settings and swapping between two different BIOS chips for boards with multiple BIOS.
No a worm can not in theory damage a motherboard, however they can damage your bios rendering motherboard unusable would have to either target a small subset of motherboards or build a large library to make the worm worthwhile,as a precaution change the jumpers to write protect your Motherboards bios
They are called eproms or eeproms
Read Only Memory(ROM) Basic Input Output System(BIOS) or firmware chips are "Electrically Erasable and Programmable Read Only Memory(EEPROM)" chips, these kind of chips can be upgraded by flashing.
ACPI Function
BIOS is not dependent on the form factor (ATX) of the motherboard. BIOS are chips with information on how to run certain hardware, these are usually American Megatrends, Award, or Phoenix.
either replace the bios chip itself highly unlikely as most bios chips are soldered or get a new motherboard as its dead a failed bios is a dead board unless u replace the bios chip (if possbile)
On a traditional BIOS, no. Some newer motherboards are starting to include a basic Linux system in their firmware, which can be used even if you have no operating system installed on your hard drive or a bootable CD.
That depends on the tool used to upgrade. Most tools provided by the manufacturer will not allow you to load an older version of the BIOS. A generic Flash utility may allow you to load an older version. Also, most Intel motherboards have a built-in BIOS repair tool that can load a BIOS from a floppy if the main BIOS is corrupted. This can usually be done safely with an older version of the BIOS.
ACPI is a function of the hardware and the BIOS. Most Pentium II motherboards do have ACPI, but you cannot add ACPI to a system that does not. If you cannot get ACPI to work, check to see if it is enabled in the BIOS.