Oh yes, it's been done! there used to be a place called beermachines.com that specialized in converting soda machines to "beer" machines! they were shut down due to copy right infringements from the brewers of said suds!
![smile](http://soda-machines.com/discussions/Smileys/smc/smile.gif)
so you're allowed to do it for yourself, but just don't try to sell them on eBay!