ady2k,
Your laptop must support booting from usb devices (i.e. floppy, cd, hard disk). If the BIOS doesn't support booting from usb devices then you must either create a boot floppy or install a loader on the ide drive. Also if the root device is on usb I seem to remeber there was a required kernel patch that delays calling init so that plug-and-pray has time to find the usb device.