Its 5700kg or a turboprop is the limit before type rating.
You can fly an Islander on a PPL MEP rating if you so wish. Or a cessna 404 but its turbine sister the F406 you need a type rating for.
Under JAR each member of the flight crew must be rated to operate. Both people have the same training and as can be seen by the ryan air thread in rumour and news the First officer is expected to command the aircraft if required.
I am not even going to try to explain the differences with the FAR's as there are many difference's depending on which part you are operating on (which i have a fleeting knowledge of).
With any luck ca-flyer will give us a brief summary on how and when two people can log time in a single crew aircraft under FAR rules. I wouldn't mind knowing anyway.
To be honest this discussion has gone way beyond private flying (my fault
) and is more into the "wannabies" with the problems they have with hour building scheme's in the US. Some company's offering 100-200 hours multi engine time for 10 000$ in single crew aircraft acting as second pilot. Under the FAR's you can log it. Under JAR you can't log a single minute of it. Which its very important to ensure that you don't have an FAA pilot/instructor on board at any point in your hour building if you can help it.
I must admit I had multiple windows open and didn't realise the post was in the private forum. I spotted hour building and thought it was a wannabie who if they didn't get their log book right it could cause huge amounts of hassel later (and quite a bit of expense and fustration). If your a pilot operating under private licensing rules it really doesn't matter.