Why not go RF wireless with an 802.11b LAN card in your PDA? You could use it throughout your house as a universal remote as well as surf the web. All you would need would be a computer based controller that would send RF to IR at your equipment. THis is what the high end Panja and Crestron units do and they are awesome. But who has $9,000 to spend on one touchpad?!

Think of the possibilites...
instead of static screens like we are used to, we could have streaming video and interactive controls in our palms.

Has anyone thought of this or tried it?

Me. I have tried to use a Vadem Clio (which has a large color trouchscreen), with an RF ethernet network, to speak to my PC via HTML that controlled my equipment. It hasn't been entirely successful, mostly due to my HTML skills combined with the Clio's web browser (both are pretty poor). It is described at my site, http://www.controlav.com

If you go to microsoft's website on pocket pc and wireless applications it talks about the wireless lan and the various options that you have, including controlling x10 units using the rf protocols.