If you have a PC running Windows and an Nvidia graphics board or chipset, download and install the latest drivers, and then download and install the 3D Vision Photo Viewer and the NVideo 3D Vision video viewer, both from Nvidia (free).

Once you’ve done this, even if you do not have a 3D monitor, you can drop side-by-side videos into the 3D Vision viewer and play them out as red/cyan anaglyph (this is how I do it as I do not have a 3D monitor yet).

You can also open MPO 3D image files for viewing – if your system is configured right, you can just double click on the .mpo file and it will open in the 3D Vision Photo viewer. I do that and have my system set up to display those files in red/cyan anaglyph mode. The conversion is automatic and seamless.