If you look around you could probably find a copy of OEM Photoshop but I'm not sure they exist and the only way for free training would be to find a tutorial website and teach yourself, i don't think you're going to find someone who will teach you photoshop for free.
With a quick google search i found this, i imagine this is along the lines of the OEM software your looking for, how legitimate this is i don't know, but shop around try and find some stuff.
I think you can get discounts if your a student with ADOBE themselves, so if your a student there's an added bonus for you!
