Take a look at this procedure for installing slackware 12 from a hard drive source:
http://www.linuxquestions.org/questi...ight=slackware
It might work for you as well, although you present a different context. Basically, you copy the /slackware directory on the dvd to some partition on your hard drive or an external usb hard drive/flash drive and direct the installation routine to use that as a source since it doesn't recognize your dvd drive. Although the slack installation routine couldn't find my dvd drive during the installation, after I did the install from a hard drive source everything went OK and on reboot, the installed slack 12 was able to detect my dvd drive.