I agree you need to reinstall. Sorry.
Here's the link (for Vista but I assume it's the same for W7):http://windows.microsoft.com/en-CA/windows-vista/What-to-do-if-you-forget-your-Windows-password
If you add that drive LATER after reinstalling Windows to another drive you may be able to browse it and look for files that you didn't want to lose. You might even recover e-mail if you know the folder (Google if in doubt).