Samstag has released the worlds first Vectrex Emulator for the PSP, heres the info from the readme:
This is a port of the Windows-based Vectrex emulator by Valavan Manohararajah known as VecX (http://www.eecg.toronto.edu/~manohv/vectrex.html). This version should run on any PSP with a firmware version of 1.0, 1.5, or 2.0.
Version 1.01 - 8 December 2005
*Added the Mine Storm rom.dat to the compiled code (to make the Eboot
stand-alone like the original console).
*Fixed the failure to display single-pixel and sub-pixel lines.
Version 1.0 - 3 December 2005
*Initial port from windows source.
*Modified original windows source for more cross-platform portability.
*Replaced Windows-specific interface code with PSP-specific code (file
handling, control input, display output).