Unless I am mistaken, you cannot open a native SW file using a version of SolidWorks that is older than what it was saved in (eg open 2006 file with 2005 software, etc.). The only way you can have your colleague view it is to save it as a universal format (IGES, STEP, etc.), but you also lose all design intent, as it then becomes a 'blob', with no features to modify .

I know it's not what you want to hear, but this is what I know from my experiences.