Don't even bother with the N64, its never going to fully emulate it (Mario 64 maybe).
As for the PS1, its using the official emulator that Sony developed for the PS1 games that are sold via PSN.
There walkthrough's on the web to show you how to convert your own games over. It looks complicated, but once you get the hang of it, its not that hard. I've currently got the following games installed on my PSP
Alundra (PSN)
Symphony of the Night (PSN)
Chrono Cross (PSN)
Dragon Warrior 7 (User created)
Final Fantasy 7 (PSN)
Final Fantasy 8 (PSN)
Final Fantasy 9 (PSN)
Grandia (PSN)
Legend of Dragoon (PSN)
Legend of Legaia (User Created)
Legend of Mana (PSN)
Lunar (User Created)
Lunar 2 (User Created)
Mega Man 8 (UC)
Mega Man X4 (UC)
Mega Man X5 (UC)
Mega Man X6 (UC)
Metal Gear Solid (PSN)
Parasite Eve (UC)
Parasite Eve 2 (UC)
Resident Evil (UC)
Resident Evil 2 (UC)
Resident Evil 3 (UC)
Suikoden (PSN)
Suikoden II (UC)
Tales of Destiny (UC)
Vagrant Story (UC)
Wild Arms (UC)
Wild Arms 2 (UC)
Xenogears (PSN)
The PS1 emulator, for the most part, is rock solid. There's some issues with certain games, but they're minor. All of the games I have listed above run great on my PSP. I'm currently playing FF7 and I'm at the 3rd disc, just finishing somethings up before I go after Sephiroth.
As for memory cards, look into getting the MS Pro Duo adapter that takes Micro SD cards. They're much, much cheaper than actual Pro Duo cards and work just as well.
Amazon has a 32GB card for $25, a regular 32GB Memory Stick Pro Duo is $54.