We actually just discussed this topic in some detail a day ago. Take a look here for some hopefully useful thoughts.

Basically this is a usable technique that can help you achieve your goal of making your app appear not to block. Just for a quick, drawn-on-a-napkin design of the app, I would think about forking first, have the parent do the Tk stuff and the child do the LWP stuff. Connect them with the socket of your choice and then take a look at IO::Socket and IO::Select for doing non-blocking communication. Also recommended is Lincoln Stein's excellent book Network Programming with Perl, which covers the two modules in great detail.

Good luck,
{NULE}
--
http://www.nule.org