Actually the PSPZX81 is more of an emulator than an upgrade really, but you'd better think of it as a course in video games history. The PSPZX81, you see, will bring all the power of the original Sinclair ZX81 (meet the beast here) and its whole 1Kb of RAM to your humble PSP, which is -clearly- not a good thing. Anyway. You'll even be able to enjoy such timeless classics as Battlestar Galactica:
Get the (free) emulator here, and some (obviously free) games here. If you really need a Sony PSP too, then get it here.
Related @ Gnome's Lair: Visiting Day - a free PSP game, 60 hand-picked free PC games, Hidden Expedition Titanic
Related Tags: Sony, Sony PSP, Playstation, Sinclair ZX81, ZX81, ZX81 emulator, Emulation, retro, games, game, retro gaming, ZX-81, 8-bit, 8bit, Battlestar Galactica