You will need a web host that supports server side scripting. (Coding will depend on which languages the host will support)
Consider carefully what functionality you need membership for and check if there are third party service providers for those functions. MSN and Yahoo both provide membership based services but people have to sign up to them them then apply to you for membership to your area.
Re: Re: Help with "Members on you site" ASAP PLEASE!
Or you can get the password gate, hide the page that they get directed to from your navigation bar, and make the address really confusing for the members page so the people can't guess it so they would have to use the password gate.