ExtremeTech shows you how to run Windows or Linux on the Sony PlayStation Portable.
To do this you'll need a couple of things: first and for all a hackable PSP (one that runs homebrew apps), a memory stick with Bochs (an open-source x86 emulator), Virtual PC or VMWare, Virtual DriveCreation Software and if you plan on installing Windows you'll need the discs of Windows 95 or Windows 98.
Bochs is an open source x86 PC emulator. Using files included with this highly configurable emulation solution enable different VGA emulation, serial port, and other IO port emulation, and the use of disk images to act as hard drives and the like. Matan Gillon ported the emulator to the PSP, complete with full-screen image scaling.