You will need to use the DNN user controller to create the account.  DNN uses a combination of the ASP.NET membership provider and DNN classes for role based security now and just adding accounts to the table is not a good idea.  Here is one article with some sample code.  You could use a post back to a custom DNN module page from the external URL to pass the user information.  You will still need to write a custom module for the registration.  Chris at Onyak Tech had a module at one time that would auto register snowcovered user purchases in DNN using a similar approach.  Not sure if it is still available to the public or not.  Maybe Chris can respond?

http://codegalaxy.com/Default.aspx?tabid=77&EntryID=5

Wallew

I don't think this will work for what I want to do.  Basically, I'm creating a asp.net web site that will create all of the user accounts for systems we use.  This site isn't using DNN.  I built it myself.  I want to add in a process to create user accounts for DNN sites we use, using specified information, username, password, etc..  I'm thinking a SQL store procedure would be the only way, but I'm not sure.