Okay, I know many have had this problem with using the [pec] (psx emulation cheater) plugin with Windows Vista. I am one of them.
If you have placed all the necessary files into epsxe's plugins folder and the [pec] plugin STILL doesn't show up on the video configuration drop down menu, then it is a Data Execution Prevention (DEP) issue.
All you need to do is go to Control Panel - System - Advanced system settings - Performane settings - Data Execution Prevention.
Once you have this screen open, select the option "Turn on DEP for all programs and services except those I select."
Once this is done, add your epsxe emulator and pec.exe files to this list.
PROBLEM SOLVED
If you have placed all the necessary files into epsxe's plugins folder and the [pec] plugin STILL doesn't show up on the video configuration drop down menu, then it is a Data Execution Prevention (DEP) issue.
All you need to do is go to Control Panel - System - Advanced system settings - Performane settings - Data Execution Prevention.
Once you have this screen open, select the option "Turn on DEP for all programs and services except those I select."
Once this is done, add your epsxe emulator and pec.exe files to this list.
PROBLEM SOLVED