I had problems with this back when I actually used my PSP.
The main problem with loading homebrew apps onto your console is that Sony don't want you to do it, and have been trying as hard as they can to stop it happening since the PSP homebrew scene popped up. Most homebrew apps will only work with a certain version of the PSP's firmware, (From what I remember, 1.1 was the optimum version to have) and degrading your firmware is a tricky and can potentially turn your console into the most expensive paper weight you've ever bought.
The first thing to do is find out what version firmware you have, you can do this through the settings (Or a name to that effect) section of the PSP. Then try to find a program that will roll it back to 1.1 (Or whatever your emulators can work with). Be warned though, these programs CAN mess up your console, and obviously doing this will void your warrenty.
Another problem is that games are often released with firmware upgrades, and will not play without them. The higher your firmware version, the harder it gets to roll it back.
(Note that this information is a few months old by now, as I haven't even touched my PSP in ages)
Still, hope that helps
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