For the price of a Pronto, why not use a Palm? It's been done before and talked about in this thread.

For serial control, you can use PalmEmpeg as discussed in this thread.

For IR control, you can use either palmremote or OmniRemote as talked about in this thread.

Not to mention all the other cool things you can do with a Palm that you can't do with a Pronto. I've never used a Pronto... is there something it can do that a cheaper Palm can't? (other than distance which is moot if you're gonna extend the IR transmitter via wire anyway).