How mobile are you looking to be? A 17" chassis will likely have a better spec at that price, but isn't going to be as easy to lug around as a 15.4" one.
The vostro range is pretty good value for the money, but are popular so the build time is quite long. Not the best looking either, if that's important.
If you look around though, the older, chunkier Vostro 1700 model can be had for a very good price, was a thread about it somewhere.