Unable To Boot From Windows 7 Upgrade Disc

I am trying to perform a clean/custom install of Windows 7 Professional 32-bit on my VAIO SZ-650N. I have the upgrade disc and though its primary purpose is to upgrade from Vista to Windows 7, it is confirmed to work with clean installs as well. Since I want to perform a clean install, I must boot the installation from the disc and not within the OS. The problem is that when I insert the disc into the drive and start up the computer, it'll pause for a moment longer than usual, as if it detects that the CD is there, like I can hear the disc spinning in the drive, and this little gray underscore will blink on the screen, but it will never give me the "Press any key to boot from CD" message and it'll eventually just load up my OS.The disc is in perfect condition and I can view its contents and run it from within the operating system...I just can't boot from it. Even the directions for clean/custom installs that come with this disc say that it must be done from the disc, not when the OS is loaded. The problem can't possibly be my BIOS startup order, because first of all the disc drive is selected to load first thing and when I insert other bootable CD's such as my beta copy of Windows 7, I can boot from it fine.

Edit: It will not let me do a custom install from within the OS regardless because it is unable to detect any drives/partitions to install Windows 7 onto. And the "advanced" option isn't there...I'm guessing because it's impossible to wipe the drive clean when the OS is already loaded.