1. at some time in 1997 model year, homelink replaced its unit to allow for rolling code technology. that unit would have amber signal indicating lights.
Are the indicator lights in the mirror amber or not? I believe the older units have green indicators, not sure though. If they are amber, it can, according to Homelink, operate the rolling code openers. If this is the case, there is an extra step to program it to a rolling code opener, this should be described in the owners manual.
Another option not touched on by Homelink is that I believe there is a converter of some type which may allow your Homelink to operate a rolling code opener, one which recieves the signal from your Homelink transmitter and converts it to a signal your garage door opener will accept. I would check with one of the larger garage door companies to see if they've heard of this device before, someplace like Overhead Door Co: http://www.overheaddoor.com/