hey ok dude, to get ure tool center u need to press modify, centre pivot.
and the reason the object u were trying to duplicate was not working is cause u had a negative 1 in Z axis is the duplcate option box. Now here's what to do.

Either combine or group your object together, Group works fine if u still want ure geometry to be seperate. which is Crtl + G
Now press Modify/Center Pivot.
Now go into front view press the Insert key. now where ure move tool was a little ball will show there. Line this up with the end of ure object Example.....where, the actual middle would be if both sides of the fighter were showing.Now go into top veiw and make sure its in the midddle of the fighter there too.Hit insert again to change back to normal mode
Now go to Edit/Duplicate/Option box. in the scale box First 1 which is X put -1.000 now hit duplicate and its done.
Add me to ure Msn mate if u have any further problems.