Probably the Kernel used on your Acme Board is already configured to have the I2C bus enabled. To check it just type:
# ls /dev/i2c* /dev/i2c-0 /dev/i2c-1
in this case two busses are already configured on your board. To know on which pins are available the I2C signals, read the pinout section of this page.
However if no device is present you have to check the Kernel drivers setup and the device tree contents.
To know how to launch the Kernel config and how to compile it follow this tutorial.
Inside the make menuconfig enable the following items:
Device drivers ---> I2C support ---> <*> I2C support [*] Enable compatibility bits for old user-space <*> I2C device interface <*> I2C bus multiplexing support Multiplexer I2C Chip support ---> [*] Autoselect pertinent helper modules I2C Hardware Bus support ---> <*> Atmel AT91 I2C Two-Wire interface (TWI) <*> GPIO-based bitbanging I2C
then compile the Kernel image, save it on the microsd and reboot.