Can't you just run the Playstation version on the PSP? I thought the PSP playstation emulator was 100% perfect, or so I've heard, I've never used it.
I don't have Devhook, so I couldn't tell you about homebrew emulators. As for Konami's PS1 emulator (used in Gradius Collection), it's nigh-on perfect.
But in order to use Sony's official PS1 emu, you have to go find this obscure client they released in Japan that lets you connect to the Japanese PSN on PC and download PS1 games without a PS3. We won't be getting it for free, apparently it will come as part of the Sony Media Manager Pro package, which REALLY PISSES ME OFF because I spent $30 on the normal Media Manager.
I wonder if I should have gotten a DS.