Ehh... hmm... if your BIOS doesn't let you boot to CD automatically (without you hitting any keys), you may have to go and get a USB to PS2 adapter (which aren't all that expensive anyways... actually, you should've gotten one with your keyboard)
You may also be able to make a diskette with universal USB drivers on it and boot to that (Although I've never had to do that... not even sure if it's possible... hopefully someone else can fill in on that

)