I'm using that board right now...
I've got it plugged into the 3v3 line on my mega, works a treat. They don't recommend it but the resistor divider built in seems to work.
on the pic:
Power and Ground are 3.3v and gnd; rest of the data lines are SPI connections as regular.
*(I should mention make sure to read the SPI side of the board (back silkscreen) not the SDIO (front side) for connection names)
Edit 6: After reading the sparkfun site comments, some people were having problems because 10k was too high for some sensors; try 1k in series with mosi and CLK...I probably should too. Not too worried about my 64MB microsd though.
