Hello,
I teach UML and C++ to engineers world-wide.
I use IBM Rationa l ROse for my corporate UML modelling (for companies such as Ericsson, Yamaha, Honda etc). and MS VIsio for freelance clients such as your self.
I would need ot see the amount of workload involved, before I can confirm full interest, time needed and budget.
What kind of diagrams are you looking for - static or dynamics. Static being class diagram etc etc; and dynamics being sequence, state transition diagrams etc.
C heers