If all you need/want to do is change every HREF from a ".html" to ".asp" extension, that should be fairly easy. Build a list of all of the files you need to change and then read that file. For each entry open the file and parse it line by line looking for HREF's. When you find a HREF, do a  s/.html/.asp/ on that line. Depending how clean your HTML is, this may/may not work as there could be multiple .html referenced on each line if it's not layed out well. If it's clean this sort of thing should work. If you have ugly HTML that is not formatted well you will have to refine things to make sure you only match what you want to change.

-THRAK
www.polarlava.com