If your system features a CD drive but no DVD drive, you can order Windows Vista on CD-ROM. The installation files span multiple discs, so unattended installations are not possible.
If your system features a 64-bit processor, you can take advantage of its advanced design by ordering 64-bit software media. You'll get the same interface, features, and functions, but you'll get them in an operating system that takes advantage of access to vastly more memory. All installation files are on a single disc. Please note that 64-bit media is included in the box with the purchase of Windows Vista Ultimate.