Hi martman101,
Unfortunately you can only use the original basic P6 in free roaming. However, do not despair.
It is very simple to make a mission, with no waypoints, just your choice of P6. Go into the mission editor and choose an environment in which you would like to roam. Find where you would like to start your ship and then choose P6 as player ship. when you try to place her you will find a window will appear from which you can choose the paint job you want from all that you have on your computer. Give the mission a name and a description and click "Save mission" and then exit mission editor. DO NOT CLICK "UPLOAD MISSION". The mission will now be on your custom missions file for you to roam to your hearts content.
If you have never made a mission, even a very simple one like this, you should read up the mission editor manual which you will find here:- http://80.95.161.114/shipsim/forum/index.php/topic,2886.msg28895.html#msg28895
Good luck and happy roaming.
I should point out that you can only do this in SS 2008 and not in SS Extremes. As you have posted in the SS 2008 board I take it you were actually referring to SS 2008.
Regards,
Traddles.