As far as I know, a command line is not part of the Vista operating system (which is absolutely ridiculous). This is because the NT kernel isn't built around or dependent on DOS, like Win98 and before were. The command line you're likely to have used in either Vista or XP is command.exe, which is not actually DOS (like cmd.exe). Furthermore, DOS cannot access NTFS partitions (without third-party drivers) and Vista is only installable on NTFS partitions, so (since Microsoft thinks that nobody ever installs another operating system on a computer) DOS would be redundant.

I think your closest option is to use the install DVD to make yourself a custom boot menu and include the recovery console on that. It's just a limited console but it's as close to a true command line you're going to get without a GUI.