Is this for a class or the like? Just curious.
Virtually everyone creates diagrams, but they normally do so with diagramming tools like Visio, SmartDraw, Dia, or Umbrello. I don't know anyone using real CASE tools today beyond that; not including the looser definition of CASE which seems to include a whole host of development tools like static analysis tools that some people seem to think CASE should include.
When I talk about "real CASE tools", I'm thinking of something like Enterprise Architect which goes WAY beyond mere diagramming and is very comprehensive. It not only helps you create diagrams, but can actually help you find issues in your design; it uses the CASE metadata to perform real systems analysis, which I think must be a key feature of real CASE tools. Visual Paradigm is probably a good example as well, though I'm less familiar with it.