The first thing you will need to do is find out details of what the server that will be hosting it will allow as registration pages will almost certainly need to use front page extensions. Many ISP's dont support Front page extensions.
The other thing you need will be somewhere to store the usernames and passwords for comparison, options include configuration files, registry and databases.
If you are requiring registration to access areas of the site security becomes a big issue, get it wrong and you might as well have not botherd creating the registration system. Ideally the passwords should be stored as a hash with a method that will has the users entered password and compare it against the stored hash.
You may be better creating asp pages or aspx pages, I cant offer any advice on asp but I know aspx pages are hosted in IIS and need the .NET Framework there are plenty of options for securing aspx pages and I can offer further advice on this if you decide to go down that route.