The latest version of RetroXMB has recently been released, which allows us to install PS3 content and run it from the XMB, just by clicking on the icon of each of our installations. With the help of this tool, we can play old games as if we were downloaded from PSN.
It's very simple. Download this package and run the "RetroPS3.exe" file, where you will also see the list of supported emulators. There is also a beta version of it, where you can download it from here.
After selecting which emulator we want to run games for, you can go to sites like coolrom.com and download roms from there. For example, let's do a test with the Sega Master System. I selected the title I wanted and download. You do not have to decompress it.
When done, you are ready to play the games. Choose "build Package" and wait. When the program is finished, transfer the .pkg file to the root of a USB Flash and install it on PS3.