If there ever was an argument for PSP hacking (and there are many), then it's this - playing multiplayer PS1 games using a pair of PSPs connected via Wi-Fi. I can't even begin to imagine the amount of reverse-engineering this feat would have required. My black hat is off to "AhMan" over at Maxconsole.net.
If you're wondering if you can download this wonderful thing in digital form, the answer (at least for now) is a rather sad "no".
AhMan would like to point out that 2-player PS1 games via Adhoc is still in a very early development. It's not even in beta yet, actually.
Is it time to go through your old PS1 games? Perhaps.