For those that can't find a blank DVD, the Windows 8 Consumer Preview ISOs can be put on a USB drive and made bootable using the Windows 7 USB/DVD download tool. Instructions are on the Windows 8 ISO download page.
Windows 8 Consumer preview - http://windows.microsoft.com/en-US/windows-8/iso
Windows 7 USB/DVD Download tool - http://www.microsoftstore.com/store/msstore/html/pbPage.Help_Win7_usbdvd_dwnTool
You might need to enter the product key to install the preview - from the FAQ page it's DNJXJ-7XBW8-2378T-X22TX-BKG7J.