It took a solid 25+ hours of work, but I finally got the MSP430F2618 to talk to the AD5933 via I2C. The TIs documentation sucks, their module sucks, and I’m angry. But it works now. A hit to those that might be stuck: The USCIABxTX_ISR() interrupt vector should be called the Master interrupt vector, and their USCIABxRX_ISR() interrupt vector should be the Slave interrupt vector. In master mode, both the TX and RX interrupt enables results in the TX_ISR() vector being called.
Other issues include that the SDA line gets stuck latched low and will persist through a power cycle and a reprogramming. You expicitley have to pull the line high in software to reset it.
A bunch of other issues later, I got it working.. I ended up picking up a new logic analyzer because of it’s improved interface than my USBee unit. $150, and it ROCKS. Joe makes them locally, and I recommend you pick one up for your toolbox.