What type of Mac do you have - more specifically, what type of optical drive
is it equipped with? Office 2008 comes on a DVD, not a CD.
If that isn't the issue, make sure the drive is working correctly by trying
other discs and that the Install disc is clean. (Use a soft cloth & wipe
from the center outward toward the edge if necessary.)
Should none of that help it's possible that the disc is bad. Contact MS -
There should be support available at no charge if you can't get the product
installed.