Toshiba Satellite A45-S150 boot usb?

My CD-RW/DVD combo drive went out, but I have an external usb dvd drive. Only, I can't seem to get my Toshiba A45-S150 to boot form the external drive. I've already had two "replacement" internal drives that didn't work...now I'm waiting on a third. In the meantime, I'd like to be able to boot Knoppix or DSL from the external drive. Anybody know any tricks?

Another piece of good news is that I have GRUB installed. Can I mount the USB 2.0 PCMCIA card or the USB 1.1 ports from GRUB? I also have a floppy drive and a usb combo memory card reader.

Thanks,

Mike B.