You can test to see if the DVD is bootable by attempting to boot from it on your other computer. If it won't boot on either computer, then it's probably a bad burn (or perhaps the
.iso image you downloaded is corrupted). If it does boot on your other computer, then the problem is one of booting your Mac from the DVD. Assuming your Intel Mac can read the DVD and has a 64-bit processor, it should be able to boot from it. (A PPC Mac will, of course, not run the Windows 8 Developer Preview, which is only available for 32-bit and 64-bit x86 architectures.) But that's not an Ubuntu question--you may want to post about that at a Mac support forum (like this one) or (since you're trying to boot Windows 8) a Windows support forum (like this one).
If this answer is not sufficient to your needs then you might want a link to the instructions you followed. It sounds from your description that you followed the instructions for burning an Ubuntu CD/DVD; there may be a different procedure that is required for burning a usable Windows 8 Developer Preview disc. You should consult whatever documentation came with Windows 8 Developer Preview.
In general, to install the Windows 8 Developer Preview on a machine that already has Ubuntu is not much different from installing any other version of Windows on a machine that already has Ubuntu. Assuming you want to keep Ubuntu, you should boot from an Ubuntu live CD, select
Try Ubuntu rather than
Install Ubuntu. Run the GParted Partition Editor. (Up to Ubuntu 11.04 this is in
Administration; in Ubuntu 11.10 and future versions, press super, i.e. the windows key, type
gparted, and click on the search result.) In GParted, shrink down the Ubuntu partition -- it's of type
ext4 -- to make room for a Windows partition to be created. Apply your changes, quit GParted, and shut down the computer.
Then boot from the Windows installation CD/DVD or USB flash drive and tell it to create a new partition in the free space you've recently created. Make sure not to tell it to erase the disk or use the whole disk. The specific interface and steps used to tell it what to do will differ from one version of Windows to the next, and may differ between different developer previews and other pre-releases of Windows 8, so you should stay sharp in the installation process. Furthermore, since the Windows 8 Developer Preview is pre-release software, it is especially important to make sure your backups of important files in your Ubuntu system are current (which you should have done anyway, before performing dynamic partition resizing in GParted to make room for the Windows partition).
Some people manually create NTFS partitions for Windows systems to use, when preparing a machine that already has Ubuntu to have Windows installed. So long as the version of GParted creating the NTFS partition is sufficiently current (as are all versions provided in currently supported Ubuntu releases), this is OK for versions of Windows up through Windows 7. However, this is probably not OK for the Windows 8 Developer Preview and subsequent pre-releases and releases of Windows 8, as they may use a version of NTFS different from the latest version supported by GParted (or perhaps the new Protogon file system).
For the same reason, you should not expect that you'll be able to read and write to your Windows 8 Developer Preview partition (or partitions associated with future Windows 8 releases) from within Ubuntu, and you should not expect that mounting it and writing to it can be done without putting the data on it at significant risk.