Your friend can save as a pm6 file from 6.5. It's under the options when you "save as".
This is real risky if he has used any of the newer features that PM 6 does not have.
All I remember is I took my PM 6.5 files to Kinkos and all they had was PM 6 I opened the files and low and behold what a mess. I had to go back and redo everything so I could out put the files. It had something to do with image frames and PM 6 did not recognize them.