Sorry, didn't realise you had reposted. Copy and pasted from your other thread:
this would be best placed in the web design forum, not just becuase it's the rule, but also becuase that's where the experts hang out.
To start you off, you're going to need a database to hold the login IDs and passwords and you'll need to use a programming language. There are a few, examples are PHP and ASP.net.
The language you use to do this will largely be determined by what your webhost allows - I think php is pretty standard, but check before you launch into any serious learning.
If you find that you can use php then google "php login script", no point reinventing the wheel you should find something freely available that will suit your needs.