Windows does NOT like booting from any external drive. ALL USB ports are "reenumerated" by Windows during the boot process, so unless you've done some serious hacking, you lose the drive if it's connected by USB. Firewire seems to be similarly not useful for booting Windows, but with different complications.
When you installed and ran Boot Camp, you should have burned the CD the program told you to burn. That CD will have tons of drivers that will allow your Mac hardware to work properly in Windows. If your DVD problem is NOT with a laptop, then make sure that a) you have ONLY a keyboard and mouse plugged into the computer and b) NOTHING ELSE connected to the keyboard. This seems to goober up the ability of Windows' preboot and preinstallation environments to see the keyboard.
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