It appears too simple so it probably won`t work but If I go to "My computer" and drag my drive C icon to my drive F and drop drive C on to drive F would the contents of C be transferred to F. Drive F is an external 40 GB USB hsrd drive. Meshuga.
Yes you can do that, however it may take HOURS or even DAYS and some files wont be able to be copied.... Also your operating system and programs wont be saved.... You need to use a program like Norton Ghost or Acronis True Image for this.... Also the "registry" wouldn't be compied to the other drive, so as "TomJerry" said it wont be bootable... And an external drive isn't bootable in anyway for security reasons...
You will probably also get a few messages about files being in use and cannot be copied properly.
If your intention is to back up Windows properly so that it can be restored, you should try TomJerry's suggestion. Or, if you happen to have a dual boot of 2 OS's (which are not hidden from each other), you can boot into the other OS and copy C from the other OS.