The SPI device I am trying to communicate with has 24bit per word communication. 8bit register address + 16bit data. How to I configure my arduino?
If you give us a little bit more information on what device you're using, we could help a lot more.
SPI is extremely straight forward. The Atmel controllers have a hardware SPI port which sends 8 bits at a time. So, depending on how your device works, it could be as simple as sending 3 bytes using the SPI port.