The easiest way of automating web access is to use WWW::Mechanize, which encapsulates LWP::UserAgent and provides among others the tick method, which selects a checkbox on a form.
You might also want to take a look at the FireFox webbrowser and the Live HTTP Headers, which will show you exactly what gets sent by the browser.
There are also two recorder tools to record and later playback a session, namely HTTP::Recorder, which turns your browser session into a WWW::Mechanize script, and WWW::Mechanize::Shell (by me), which gives you a command line interface to your browser, and turns that command session into a WWW::Mechanize script.
