Here's the source code for Zdoom
http://zdoom.org/files/zdoom/2.2/zdoom-2.2.0-src.7z
Zdoom supports Doom, Doom2, Heretic, and Hexen...custom resolutions(so it'll be easier to make 480x272 without the distracting offset on Heretic), OpenGL, and other nice features.
Quake PSP runs full hardware on 222 flawless, Zdoom should be a breeze for the PSP to run.