As promised I managed to build a Homeseer plugin. The plugin works by capturing RS232 commands it gets from the TSU9600. The commands that are pure text can then be used as triggers for anything you like in Homeseer.
Currenly I control my X10 lamps using it and I also got it to tell the time when I press a button on the remote!

I'll put up a webpage later and see if I can't get it out through Homeseers proper update interface later. But for the ones that want to try it before hand you can grab the plugin called HSPI Prontonic right now.
Unzip the file into your Homeseer dir.
Go to Setup->Interfaces and Enable 'Prontonic'.
If you then click 'Config' I have written a small tutorial on what you need to do.

Also as a side note I found another thing that causes the 'Invalid command' error. If you have multiple extenders set in the Pronto Pro editor to the same IP you will get that error.

Cheers
Joakim E.