Your question is a bit lacking. What kind of I2C-USB module? Or rather does it come with a Linux driver? If it does you probably won't need to write one. An application will do. You can read more about I2C and SMBus here.
Basically what you need is the I2C address of the control board (a single byte). When you have the address you (as the master) issue read commands over the I2C bus to the control board using its address and reads the response. If there's a driver for the I2C-USB module this should be straightforward enough. Plug in the device and open() the device (/dev/[i2c-usb-name] where [i2c-usb-name] is the name of the device). Then follow the driver implementer's guide how to setup and send data over that device (typically using read()/write() or ioctl()). Here are some additional information on working with I2C from user space: http://www.mjmwired.net/kernel/Documentation/i2c (select topics in the menu on the left hand side).
If you must write the driver yourself, the first stop for a Linux device driver beginner is the LDD3. Read it, it's quite a pleasant read.