It's a CrMo frame, 1" threaded headset (Shimano 600EX, the kind that says "Sealed Mechanism" even though it uses ball bearings). I don't think a picture would do much good- it just looks like a stem inserted into a steerer tube. The problem is that I can't get it tight enough because it uses an expander instead of a wedge.

Edit: Thanks ubrayj, but I have not noticed that the expander has a notch in it at all- that would certainly solve my problem! Perhaps I will start looking for a replacement expander wedge that does have the notch. It would make sense to have one, there is certainly a good place where it would fit in the quill itself. Either way, I'll try your method tomorrow and see if that helps. Incidentally, how secure can a quill stem get? I've definitely seen wedge-stems lock into place so tightly that the apocalypse could not set them loose (not frozen, just well tightened), but this expander stem seems to have an upper limit of security on it... weird...

mtnwkr: Thanks, I did see that on Sheldon's site but this is definitely not the problem! The frame is a 63 cm and the head tube is as long as my forearm. Thanks though.