I don't think you'll find anything like that for under $400 if you want my honest opinion. Plus with a used laptop like that, you'll find that the battery can only take two thirds or only half a charge. The screen is only XGA with a few dead pixels, and the overall system is not in the best of condition.
The BestBuy in my area usually gives out flyers in the mail, I would look there first only because I've occasionally seen a nice Toshiba Laptop for $789 on sale. I would try to save up a little more money and buy something that will last a little longer then a used laptop if I were you.
If you're still adament about getting a used one you can try the following:
HOWEVER, before you buy from any of these dealers, be sure to look them up on reseller ratings FIRST!