P&N mod with patched TDM AIs is a good choice for lots of small changes to the game that really add up.
You have to add an attack ship design to each of the races' AI_Ship_Design.txt file that is 3500 kT in size (and a good design, of course), so that they will be able to design them. Once they design them, they will build them (unless in the early phases when they have a max tonnage of ship they will build).
For more information on modding the game (although it is not about AI modding, just the data files), check out
SEIV Modding 101: A Tutorial.
[ December 11, 2003, 23:30: Message edited by: Imperator Fyron ]