Way back in WinXP times and before, I would always connect all of my PCs at one desk together to a single set of speakers. The only special software/hardware this required were some extra 3.5mm audio cables and a set of ordinary speakers. The software to do this was built into Windows XP and just required some intelligent checkboxes to be selected. However, the native ability to do this with both Windows Vista and Windows 7. Luckily, with a registry hack, it is possible to still get this behavior with both operating systems!