Use something like HTTP::Proxy + HTTP::Recorder + WWW::Mechanize and/or WWW::Mechanize::Shell to record a manual submission. Take the resulting generated script and modify it to do the task more than once. (leira's article "Web Testing with HTTP::Recorder" contains an excellent example of how you might want to do this.)

If the web service you are using requires javascript, then you'll need something else (like Win32::IE::Mechanize) - Super Search this site for "mechanize javascript".

Another important tool for finding out what is really happening behind the scenes between server and browser is a protocol analyzer such as Wireshark, or, if you are using Firefox, something like Live HTTP Headers.

You may also wish to peruse the site in question's Terms of Service to see if what you want to do is permissable; also, putting in some sort of delay between fetches so you don't hammer the server into oblivion might not be a bad idea.