Didn't say what kind of processor you're running, but there's a sticky thread on AMD dual core CPU's
here.
I like to keep peace with the other races until the end of the game when I'm ready to conquer the board. There are some tricks to keeping other races from attacking too early.
Keep an eye on your relations through the diplomatic screen. Check relations every few turns. Relations will move to hostile before a race declares war.
If you play "good", you don't get as may bonuses, but it improves relationships with other good races right out of the gate. That's half the universe you'll have an easier time with.
Although it's better to colonize higher PQ planets first, aliens get touchy when you share star systems with them. Try to claim all habitable planets in a star system before the other races get to them. One trick in doing that is to buy a starport on a newly inhabited planet, then buy a colonizer with nothing but a colony module on it. Load a few colonists and send it over to that neighboring planet.
Go for those yellow diplomacy techs. Diplomatic bonuses make it easier to maintain good relations.
Trade with the other races. Trading improves relations. Set up trade routes with the ones that are harder to please. Buy techs off them. If you see your relations falling off with a particular race, pay homage to them with cash or other gifts.
Some galactic wonders and special projects are "must have" Watch for those. They become available when you research various techs. The detail view of the research screen tells you what techs provide what bonuses and projects. Galactic Bazaar and Spin Control Center are two I can think of off hand. Restaurant of Eternity is a good one. Diplomatic Translators are a big help.
Military strength improves relations. It's sometimes the only way to keep the Yor and Drengin at bay. If they are afraid of you, they will suck-up. Start building military ships when you see other races doing it. (look at the graphs in the cockpit of the main view). I take a medium hull and stick nothing but missiles on it. Then I build them and leave them in orbit. They're cheap to build and they give the illusion of military strength when actually, you have little.
Don't put military ships in alien space until you are ready to fight. A few troop transports too close to alien space can cause them to declare war. I keep them parked next to my planets, then line them up along the borders of my space just prior to invasion.
Take advantage of war you are not involved in. You can form an alliance with a losing race providing a high change they will surrender to you when they give up. Wait until you see their military strength getting close to zero. Then form an alliance and supply them with ships and cash to improve relations. You'll inherit their remaining planets. If your alignment is very good, you get the Concepts of Righteousness tech. That tech provides a project called Hall of Empathy which further improves chances of alien surrender to you.
Ok, have fun!