The IRDA port is not suitable for IR transmission or for receiving consumer based IR signals. It is only good for short range computer device to computer device ccommunication. See the links below.
Allthough that sounds like interesting idea... i bet your easier option is to do what everybody else: use XL client on tablet via wifi to command your main XL system which in turn uses USB-UIRT (or similar infrared-infrastrukture) to command actual devices on your setup. If lag (trust me there will be) caused by that doesnt turn out to be too anoying. If thats the case some of those earlier ipaqs can serve as both direct infrared universal remotes and hosts for xlobby client to run on.
That works great. The lag is almost non-existent for me. My HTPC is not always on. I had hoped to run full XL on a tablet when just using cable boxes and not a full blown media center and have a "fancy" touch screen remote for any room in the house by having a screen or two for each area of the house. Then when using full, just start the tablet as a client instead of server.