O.K. before I do anything.......let me see if I got this right?

I want 3 image sizes. say 75x75 100x100 and 150x150
For them to zoom I just say upload the max size or larger (150 or 200) and then imagehandler will shrink it so to speak. But it doesnt enlarge....is that right. Told ya Im a noob to zen. (if it werent for phpbb Id be even more lost)