Cant install Leopard, the installer tells me to clean the dvd

trying to install leopard from the official apple Leopard install dvd, all new, received this morning, i get this error after 5 minutes of install :

"There was a problem reading the Mac OS X Install DVD, carefully clean the disc and try installing again".

My dvd reader is working fine, i dont knwo what is the problem, the dvd is not damaged.

what should i do now?