Emulation itself is legal; however, downloading copyrighted game files (ROMs/ISOs) from the internet is considered piracy in most jurisdictions. Always use your own physical game discs to create backups for use with emulators. step-by-step guide
Here is a short story about the dangers of chasing a "too good to be true" emulator. The Ghost in the Machine esx ps3 emu 097r5567 portable
For modern PS3 emulation, is strongly recommended. This ESX portable version is preserved for archival and legacy testing only. Emulation itself is legal