You know you're dying to play an old System 7 version of Oregon Trail on the go. Admit it. That's why there's Basilisk II, a 68k Mac emulator for the PSP. Basilisk can run systems 7.5.5 through 7.6.1 pretty decently. You will need a mac.rom file to legally run it, but we all know you've got that laying around someplace. You'll still have to wait awhile for Basilisk II to work like a real old-skool mac, because right now only emulation, video, and a few inputs like a mouse work. There's no ethernet, audio, keyboard, external filesystems, or serial capabilities either, so it's kind of useless—but worth watching. You'll also need firmware 1.0 or 1.5 for the PSP to run Basilisk II, because 2.0 just isn't gonna cut it.
Basilisk II - Macintosh Emulator [PSP Updates]