Need to know a budget. Most newer systems with an A8 or an i5 CPU will handle SIMS 3 pretty well. I would not go lower unless you are OK with lower settings or lower resolution which you probably won't want.
And since non-gaming grade laptops are not upgradable easily if at all, you will be stuck with what you get for a while, so better to spend an extra $100 or 200 on something good than wish you did.