Hum, you should disable the anti-virus too. And 512 mb? Isn't the game recommended for 1Gb of ram? I have 1GB of ram and an Athlon 3000+. I'm playing at huge galaxy with crippling AI and i did not notice much difference. I do have a Geforce 6800 GT as a graphic card, which must help some.
The eye candy is nice but does not give much to the game. After a while, you just don't notice it anymore so you might as well turn it off. What they should do is take the time while i'm doing my turn to crunch some AI so that when the ai play, he does not need much more time to do his stuff. Of course you will have to give priority to the stuff i'm doing, like moving my ships and attacking, but still it would be an optimization over waiting for the ai turn.
Oh and i've notice a little bug still present with the latest version. The Torians seems to make a check point where they send most of their ships and they just sit there, doing nothing and not assembling into a fleet and coming after me like they should. This was reported waaaaaaaaaaay before the patch so i tought it would be fixed. Granted, i have seen it far less often, but it still happen.