Hello sweet Baby Jesus,
(I enjoyed typing that!)
By itself Final Cut Express can't do automatic motion tracking.
If you want to highlight your face and have the highlight object follow your face manually then I'd suggest the following:
1. Create a circle object in Photoshop and make sure to save it as an alpha layer so that the centre of the circle has a gap and not a background.
2. Add the image (.png file) to your Sequence on a new video layer.
3. resize & position it to taste and switch the canvas viewer to wireframe + video mode.
4. Double-click it to view it's parameters and start adding key frames for it's position. Move along the time-line and when the face moves from the circle, create a new key frame and move the circle object as needed.
It can be a pretty manual process, but some key commands will make it easier. I'm not near Final Cut right now, but let me know if you need any help.
If you'd prefer a more automated process, then After Effects is great(!!) -- alternatively, there are plugins available for Final Cut Express which you can try googling.
http://www.colinlevy.com/tuts/IcarusTutorials/Icarus.php (Free apparently - but a separate application)
Hope this helps!