DOSBOX runs slow on a full fledged desktop. If you want to play Dos games on the PSP, you be better off writing an interprepter for game files (eg SCUMMVM for SCUMM games). OR a better Dos emulator from scratch (not sure that's going to happen either).
There is no one defenitive guide to port a game/emulator/etc. In short, you grab the source, find the platform specific code and rewrite it for the new target platform.
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