I have found a emulator (a VBA) for my ps3 and it ends on .pkg. Is there any fast and easy way to unpackage it?

In most cases package files can be installed from the systems package management software. This applies to Unix-Linux based Operating systems. The contents of the package can be viewed and extracted using a archive manager found in Unix-Linux based systems.
With the PS3 the package you are looking at may assume you have modified your PS3 in some manner before hand, do some Googlefu and see what dependencies are required to install and run the software on your system. Remember that in many cases with consoles that altering the operating system may cause other software to stop working or may void any warranty.