Heya, if you were hosting a QuestNet game on your own dedicated server(like an extra PC of yours), then it would be entirely possible to have signups through a website. The simple part would be setting up Questnet to use a login file, it already can do this and stores the usernames/passwords in a plain text .qlf file. The slightly more difficult part would be having your websites registration script add a line to the .qlf file, but the formatting is straight forward and simply username;password.
A simple way to do this would be using PHP. W3C Schools @
http://www.w3schools.com/php/default.asp is a great place to learn PHP on the web completely free, and with the lessons there you could easily create such a script in a matter of minutes. Specifically check out the PHP File lesson under PHP Advanced.
I'll take a second and plug a website I'm just now getting up on it's legs,
http://www.questdev.info, which aims to provide easy to follow ASL references and tutorials, though honestly is completely bare as of right now. Perhaps I'll make persistent accounts, properties and inventories some of the first few tutorials.
Hope that helped.