A lot depends upon whether or not you want your clip art to be an overlay (like a picture frame), or an actual picture.
If you're using it as an actual picture, as though it were a video clip, just open the file and add it to the library. Then you can plop it on the timeline wherever you want it. For this purpose, it can be a GIF, JPEG, or PNG.
If you want the underlying video to show through, then it has to be a format that supports transparency. That means GIF or PNG. In this case, you would import it to the library in the same way, but you would put it on a PIP track. That would make it an overlay.
The thing to remember about the tracks is that they are like a stack of slides. Imagine that you have a picture of a naked woman, a picture of a dress, and a picture frame.
I'm going to ignore the "special" tracks like voice-over.
Now put the picture frame on the first track, the dress on the second track, and the naked lady on the third track. What you'd see is a naked lady standing in front of a dress, with a picture frame behind them both.
Now put the dress on the first track, the naked lady on the second track, and the picture frame on the third track. You would now see a nicely framed picture of a naked woman standing in front of a dress.
Now put the woman on the first track, the dress on the second track, and the frame on the third track. Now you have a framed picture of a woman wearing (or at least standing behind) a dress.
For this to work, all three need to be transparent in the right places. You would probably put a background on the first track and move the other three pictures down.
As for using Director Suite 2, I'm not sure that PhotoDirector is good for making clip art. I usually prefer a vector-based drawing program that lets you draw and alter shapes, group them together, etc.
If you're talking about the kind of clip art that is photographs, not drawings, then PhotoDirector should be able to do the job for you. I've never used it, to be honest. I have another program that I prefer.
Jerry Schwartz