JMich: No worries. This is more or less what amok was saying on the legal parameters part.
To be able to emulate a console, you need to secure the legal rights to use that console's OS, something that atm hasn't been done (I think). So if a site sells you the equivalent of DOSbox for PSOne, it does need to have legal permission from Sony to use the OS for the emulator, plus (of course) the emulator and game distribution rights.
I am not sure how many console emulators are currently in existance, maybe someone else can answer that.
Half correct. While many PSone emulators require the use of the copyrighted BIOS, there are emulators like PCSX that use high-level BIOS emulation to negate the need for an actual BIOS. Clean-room emulation of the BIOS is something that Sony would not be able to do anything about.
NES and SNES emulation would be no problem, as long as mentions of Nintendo are removed from the games. PS1 a little more tricky, as the Sony references are more integrated into the games. And in the case of the early Tenchu games, I think Sony has exclusive distribution rights anyway.
I think we're done here until you can learn to be a little more polite.