Zero budget eh... ok, what you like with a soldering iron.. A quick google I found..

http://www.instructables.com/id/IR-R...your-Computer/

Maybe you could knock something together like that and write a C++ driver, "shouldn't" be too hard given the nature of linux and the supporting community, am should you would find help or even someone who would do most of the work as it's a good idea...

I'd would suggest that the adverts are a set length, as most people sell advertising based on time, so you could in theory hit button on the remote that starts a timer of sorts which blanks the screen plays some background music (easy enough in a bash script) for a set length of time, and then revert back say maybe 2 secs before the end of the advert..

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Thanks... Simon