Not sure how the test OS got on there, I thought it had to be specifically loaded onto it, and it replaced the normal OS, maybe that is not correct, or maybe your mate was having problems and tried to work out what they were by loading the test OS?
Maybe someone else will correct me, and tell you that you can get back to the normal OS without reloading it, I am not 100% sure.
You load the OS by loading it from the load screen, from an attached storage device, or by holding down the window button when powering it on, which might be only from CF card, and which is probably the only option with the test OS on it.
Alternatively, the test OS might be on a flash ROM installed inside the MPC, but that seems like an expensive possibility...
http://www.mpcstuff.com/1a771314j.htmlKeen to get a copy of the test OS.
No, sorry, 3 hours South of you (with way too many MPCs!).