I use rose2000e to design my system. I think the deep understanding of oo is key to get a perfect design. And some tools is helpful to coding. such as Rational Rose J Tech Preview, Rational Rose J to IBM VisualAge for Java, and Ensemble Rose JBuilder Link 3.x.
to study UML , you should study UML standard first,
the RationRose is only a tool to implement UML.
for java developer, using TogetherJ4 tool instead of RationRose (only my suggestion)