The AI in my past couple games has done pretty much nothing at all. None of the AI races have colonized outside of their home system. The graphs for research, industry, etc. are completely flat. The only sign of activity I can see is an AI scout/flagship wandering around every now and then.
My earlier games didn't have this problem. The only difference that I remember is I kicked the difficultly up to "tough". I was playing on challenging before. Randomize intelligence is also turned off.
I'm playing DA 1.61.090 on Windows XP x64 dual core AMD.
I'd be happy to supply a save game or anything else that is needed. Just let me know what you need.