Well in general our focus is not on Fighter vs Capship combat. In general it'd be highly unlikely if not impossible for a lone fighter to take out an ISD, even with help. That's not to say it's invulnerable, but your role in a battle would be more to pick off subsystems and the like than take the sucker down. However, the ISD isn't great at fighter defense. It's mostly armed with Turbolasers which track too slow to be used reliably against fighters, but it does mount enough point defense guns to make you think twice about taking it on. The best strategy for this monster will be, of course, the TRD strategy (Trench Run Disease). Get in close enough to the sucker to skim along its hull and its guns probably won't be able to track you if you keep moving quickly. Getting that close, however, will be tough.