Are you writing a .NET application to communicate via serial/Ethernet with a .C program running on the BL2100?
You use Dynamic C 9 to compile .C files. You can either compile directly to the board, or compile to a .BIN file that you can install with the Rabbit Field Utility (RFU).
There are sample programs you can use as a starting point to create code for the BL2100 to communicate serially, or to open a UDP or TCP socket on the Ethernet port.