I think the key would be to identify a suitable IO module to control the gates open / close events (presumably connected to relays that trigger the gate event). You'd probably also want some form of limit switch to identify the gates current state. probably through a slotted opto switch. no to sure if you'd need the limit switches, you could always wake the system and set to a known state (presumable gate closed).
there's lots of suitable contenders out there including the likes of
Weeder Technologies RS-232 Data Modules
there's more robust ones out there in the form of a 432 industrialised network
as to how sophisticated it needs to be I dunno, depends on how many gates there are, how reliable the mechanism is.
I'd probably want to have a two button by pass switch somewhere, so you could trigger each door to open or close as required just in case the computer(s) went tits up.
having established the hardware you then need to read or write the correct settigns using their drivers
I'd rather be riding on the Tiger 800 or the Norton