The wiring sounds correct. You didn't specify the direction of the diode. If placed the wrong way it will short circuit the Relay. It should "point" from the negative to the positive relay terminals so it doesn not normally conduct.
under Relay Driver Outputs
You can just use the Digital IO Screen to test. All you need to do as set as an output and toggle the state.
From C code it would be:
SetBitDirection(0,1); // set bit 0 (Relay0) as an output
SetBit(0); // set bit 0 (Relay0) on