I'm trying to run one of the AI scripts to get my opposing zerg force to act as aggressively/hard as possible, though I'm not sure which one to use / which script does what.
I tried using the "Zerg Insane Campaign" trigger to see what happened, though he seemed to die off after he made a few overlords..

Hi!

Campaign scripts expects the cpu player to already have a base. Custom's creates bases. You can always spawn units and trigger their "own" AI's by ordering them to attack this, that, other target whenever a condition is set, but that is the hard way.

Also make sure the computer's race setting matches the units/AIs you give him or he will just mine.

Melee computers use the Custom AIs, however, the most difficult AIs, ones that will use whatever resources you give them, are the Insane AIs, first of all, you have to do as Nude said and make sure the race matches up with the units, and the AI being used, not just 2 of them, all 3 must match or it will not work.

Secondly, the Insane AIs are meant to have a bit of an advantage, and work well if given extra money and a starting base to begin with.

to make them hard on the insane level, give them a big boost of mins n gas