Booting from a CD-ROM is a simple process from my experience. So long as you've told your BIOS to "Boot from CD-ROM" then all you need to do it put the disc in the CD-ROM drive as soon as your computer starts. It'll then load the CD and give you the options from there.
Most BIOSes already have the boot from CD-ROM set up so you shouldn't need to do anything more than put the disc in.
However, if you are actually capable of running your system, even if you do have a virus, then I'd suggest you just install Norton AntiVirus onto your system and run it from windows.
I believe the emergency start-up from CD-ROM is just for systems where you cannot actually stay in the Operating System because of the virus.