Not sure if you meant that the CD wouldn't boot or if the laptop is unable to boot from USB. Not sure if it will help but there is a version of slackware called zipslack which you can boot from a zip drive....never tried a USB cdrom myself before.
Here's a couple of links that might help too: Booting Knoppix from a USB Pendrive via Floppy http://www.tldp.org/LDP/LGNET/current/okopnik1.html and Booting a "Live CD" image without a CD http://www.tldp.org/LDP/LGNET/current/tag/2.html
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