Dell is an excellent choice, but you might want to look at the Dell Precision Mobile Workstations rather than the XPS, which is more of a video game machine than a production machine. As long as your stats exceed the recommended requirements for AutoCAD, you should be set. Your price range will be no problem.
I just purchased AutoCAD LT 2012. My Dell laptop is a 32 bit and the install requires 64 bit. Does anyone know of a way to install without my having to purhase a new computer? Any help would be appreciated.