Northbridge and Southbridge are supporting chipsets that are permanently soldered to your motherboard. You can usually tell what they look like because they'll have a heatsink on them. Most these days use copper or thermal pipes. Pretty neat looking if you ask me. You cannot upgrade these so when choosing a motherboard, always look for what chipset you want. Via chipsets are mehhh. Choose between Intel and Nvidia chipsets. Try to pinpoint them on the motherboard with the description I just gave you.
BIOS is another permanent chip on the motherboard. BIOS stands for Basic Input Output System.
All computer hardware has to work with software through an interface. The BIOS gives the computer a little built in starter kit to run the rest of softwares from floppy disks (FDD) and hard disks (HDD). The BIOS is responsible for booting the computer by providing a basic set of instructions. It performs all the tasks that need to be done at start-up time: POST (Power-On Self Test, booting an operating system from FDD or HDD).
Oh bloody hell, I'll just give you a pict of the Northbridge and Southbridge since I just ate a big bowl of spaghettin and meatballs: