You have to switch the DOPPLER-INS SWITCH ('707 Captain' FLIGHT MANUAL Part II - Aircraft and Systems (cs707_manual2.pdf) page 22) to INS, then the AP will follow the INS course once you turn the Mode Selector Switch to NAV. Make sure to open the SimIcons Panel using SHIFT+1 to initialize the CIVA INS after the aircraft first loads in FSX, or it won't work.

CoolP has a Topic on dual INS, and a whole bunch of other info, here: http://www.captainsim.org/yabb2/YaBB.pl?num=1285100008. I highly recommend that you read through it for help with the CIVA INS. ;)

Mark