I think it's actually Windows that upscales, but you are right in saying that some gains can be made from upscaling using specialised software. Photoshop's upscaling algorithm is generally considered excellent, and there're also additional parameters that can be used to produce a slightly sharper image (not much different to using an unsharp mask).
With that said, the quality is still going to be a far cry from the kind of masterpieces Laser has been putting together as his sources tend to be high quality and he does a lot of hands-on work to get them looking great. It's that hands-on work and restoration that has really made this thread special, particularly with pieces like the MI1 box art that had the the logo removed and the Grim Fandango mural that was previously only available creased on the inside of the CD insert.
I think if you've got no other option or the time to do a more thorough upscaling job it's acceptable to just do a basic upscale, but the results are going to be negligibly better than just letting your printer software/Windows handle it and most people can probably do that themselves.