I think that most guests don't know the difference. They are happy as long as they can find a browser, Skype, digital camera program, and messenger.
I used to block people from using Internet Explorer and a common question was, "Where is the Internet?". People didn't know "how to find the Internet" because the blue "e" icon was missing from the desktop. So I put the blue "e" back on the desktop but made it launch Firefox instead of IE and the problem was solved. :D
All they cared about was finding a browser, and it didn't matter what browser.
I think the tech savvy people who care about what software they use probably travel with their own laptops or netbooks.
I think Ubuntu Linux* would work well. I think most people won't know the difference -- but if you want to charge for Internet, most of the billing programs are made for Windows.
Free Software for Hostels
* (the Wiki page is a work in progress)