The book I have on this suggests that a class (or book) on complex analysis will be useful preparation.
A book is on the way, just ordered from AbeBooks. "Complex Analysis" by Lars Ahlfors, 1979. This is a graduate text, reputed to be fast paced and notoriously difficult. It is also said to be superb, elegant, and comprehensiveTom's Dutch Oven Info / tom@mmto.org