What are you using for your members area? Do you send username and password instantly after payment or do you sort this out manually for each person that has paid? (I'm talking about Clickbank members that have created a product and sell access to a members area)
a lot of people use the same username password for everybody. for example, on the thank you page you just have the username and password there to log into the members area. hope this helps
hire a developer to write a script for you. using the same username/password for all your members is just asking to get it leaked on a internet forum somewhere, and what will you do then? you can see my custom solution at: http://www.gainopinion.com
Or after your customer has paid, you could redirect them to a signup page for your membership area. And you could use a free or paid script for your membership area, depending on your requirements...
all you have to do is use a member management script that has a validation field. you have the member register on your site, then the script emails them a confirmation page that includes a ClickBank payment link once they land on it. the link to ClickBank should contain their member id as a query string parameter. when the ClickBank payment has been made ClickBank returns the customer to your thank you page, along with the query string information that you sent along. you check the query string and see that it has a ClickBank order id (indicating a successful payment--there is even a signed variable you can inspect to ensure the order id is legit). then you validate the members account on the spot (i'm assuming your thank you page is a script that can process the information from ClickBank). so this is all done automatically and every member has their own username and password. i wouldn't say easy peasy, but i have coded this kind of thing myself. it's not that hard.