PCSX2
The Bios you have to get from your PS2. However the PCSX2 Emulator guide will assist in downloading and setting up the system
Not without an emulator and downloading the game disc into a file
PCSX2 is the only PS2 emulator to consider and they are working on Version 9.9
The related link has the emulator and a guide for downloading and setting it up
See related link for a guide to downloading and installing the PCSX2
No the Xbox could not run an emulator for the PS2
No, a DS emulator is not compatible with the PS2
no. you can only play ps2 games on earlier ps3 models that had the ps2 emulator
just downloading a ps2 emulator and download a ps2 game to order to play the game. It is not anywhere near this simple nor does any PS2 emulator work except in a beta or test version. The best rated emulator is the PCSX2 and it does not even allow you to start many PS2 titles. After the PSCx2 is downloaded it needs someone with real computer skills to start the set up process after you locate a copy of the PS2 bios.
It is not just a file and you have to sort of turn your PC into a PS2 by downloading your copy of the PS2 Bios and a emulator program called PCSX2. see related links
Read about the PS2 emulator on the related link
There are no working PS3 emulators. The PS2 system has some poorly working emulators that can barely manage to complete some PS2 titles with a lot of work and very poor results on over half the titles. The much more complex PS3 system does not have a working emulator, but it could still be illegal to download Sony Software if it was included in the emulator even if the emulator does not work