I would like to create dynamic images from html that I\'m generating on website. I have code that generates a PSN Trophy Card, ab Xbox LIVE Gamer Card, a Steam Gamer Card, a
You'd need some page rendering library or service. Litmus is one such service I've heard about. You might start there.
If you need to take a screenshot you will need to do so client side. So you will need to do so using some client side tecnology like javascript, flash, silverlight... Asp.net runs on the server so it is ruled out.
Here are some links to other related SO questions about taking a screenshot with javascript:
JavaScript code to take a screenshot of a website without using ActiveX
Take a screenshot of a webpage with JavaScript?