So, you want it to play modern games? Such as....? If you mean graphics-intensive games, you will find it hard to find such a laptop in your budget. However, many modern laptops are so far ahead of my £650 laptop that I bought a year ago (about $1200, considering you can acquire technology cheaper in america), so I think you should be able to run Civ4 great on a laptop in your price range. Make sure you avoid Intel Celeron M like the plague, it is cheap and no good for games. The Intel Centrino Duo is what you want. Also, look for 2GB of RAM (hard to find in that range, but possible) where you can allocate 256MB to VRAM. Unfortunately, at your price range, it will be hard to find a laptop with a dedicated graphics card, but 256 MB shared graphics will work well. 128MB if you must, it is good, but not for modern 3D games. And if you can't get 1GB of RAM, you can always fit it yourself for possibly $100-$200.
That's my thoughts on your situation, anyone else agree, or have more to add?