Vista"s installation process is dramatically different to any previous version of Windows: rather than being an "installer", the install DVD is actually a preinstalled copy of Windows that simply gets decompressed onto your PC. It is hardware agnostic so it can adjust to different systems, and you can also install your own apps into it so that your Vista install becomes a full system image install.
There"s an interesting in-depth interview with a Microsoft Australia tech specialist here as well as a story that looks at some of the pros and cons of image-based installs here.