You could probably sell it for 300 dollars.
It is a decent computer. Older... But is decent.
The problem is, it was meant to be a gaming pc and today's gamer won't be too interested in looking for something like that.
If you were to sell it, aim to sell it for 450 dollars, and bargain with buyer from there.
But it really isn't worth much considering that GPU is weak, processor is okay, screen resolution is horrible, and it has Vista.
Just stay positive, call it a Used gaming laptop for $___