Do you just want to look at the new stuff DOM nodes created by the scripts or do you want to control the whole process with perl. If you just want to look (and mess about by hand) check out the firebug firefox extension.

If you want perl control, check out Mozilla::Mechanize::GUITester and/or Mozilla::Mechanize or WWW::Selenium. update2: Win32::IE::Mechanize

update: just to be clear: LWP does not support javascript at all, and as far as I know no-one is planning on adding javascript support. All options I linked drive conventional GUI browsers since that's a lot easier to build and support than creating your own compliant and effectively useful DOM/BOM with javascript support. I should know - I gave it a try once :-)