I think I get what he means, but let me also explain. I'll copy what I told another member to do...
First of all, start up MM2CT. Then, click "File", "Open PSDL", then browse for your city PSDL. On the box on the lower right, you should see 4 tabs above it. Click the one that says "Props". Right click anywhere in the white area, and click "Add object (single)" Then, browse for the object. and import it. After this, red text should appear. Right click the red text, and choose "Add position". After this, you should see arrows appear in the lower left corner. Use these to move the points around. Also, look at the text below the arrows. It provides information on how to do it faster, slower, ect. Use the up and down arrows to adjust it's altitude (Or Hight). The diagonal arrows move it along the Z axis, and the left and right arrows move it along the X axis. When you have a good starting point for it, right click the red text position (The one that has "Base", and the numbers after it) that is in the white box I described earlier, and click "Duplicate position". After this, use the arrows again, to move the new point around. Continue duplicating, until you have a good path. The object will travel from the end point to the start point when it hits the end of the path, so make the end point, and the start point look like a continuing path. Then continue this whole process to add as much moving objects as desired.
I'm not sure how you would want to save it, so I will tell you what each name does...
*_sailboat.pathset - You cannot hit the object, there are no sounds, and it goes about 10 MPH.
*_ferry.pathset - You can hit it, there are barge sounds, and it goes about 2 MPH.
*_train.pathset - You can hit it, there are no sounds, and it goes about 100 MPH.
This one is different though, it goes from point A to point B. I also have never had any luck in getting it to follow the path correctly though...
Hope that helps.