Is there any specific reason for it having to be a laptop? Building a desktop for the same price would give you much better performace.
Runescape can be run on almost anything, the nvidia three series was introduced around March of 2001 (I think) so almost any inbuilt chip should be able to run it.
GTA4 for the pc won't be playable on any laptop with a decent framerate, at least not one that's out yet. (The new asus model may be able to when it's released but that's hardly relevent)
Call of Duty, although not very demanding, won't play well on laptops. The graphics chips in laptops carry similar names as their full sized counterparts but are not as powerful. I wouldn't expect to be playing this with acceptable framerates, especially not in that price range.
I'm not trying to steer you away from using a laptop for gaming, but they are often more expensive and less powerful than a desktop.
If you search newegg.com or an equivalent im sure any laptop in your price range with be sufficient to run Runescape, assuming these laptops aren't more than a couple years old.