Actually, there is some software that does exactly what you require. The link is: [Link: veg.nildram.co.uk]

However, you will need to build a very simple circuit to act as sampling hardware (the IR port can't do this). Once you've got the samples (which work between computers), you can play them back using either his matching transmitter circuit or an IrDA port. It works perfectly; I'm using it right now. You may want to consider building his transmitter circuit to get better range, but on Sony VCRs and the like, the IrDA port on my laptop works over two metres or so.