What you define as "good" depends on what you're looking for in a laptop.
Given your existing machine, I wouldn't worry about absolute gaming performance. It would be redundant unless you expect to frequently spend days or weeks away from your desktop.
Upgradability... don't expect it. Technically, both ATI and nVidia have their own video upgrade solutions, but they're not really interchangeable and you can't count on there being a module for an upgrade by the time you're ready. On most laptops you can only ever upgrade the RAM and hard drive, and in the case of the latter you'll likely void the warranty (since you have to disassemble the case).
What kind of programs do you want to run? That's probably the most important question, since it dictates what kind of laptop you need. If you're just browsing the web, listening to music, and so forth, you don't need a fast video chipset or even a large screen. I find that Apple's 12" iBook is good if you actually use it as the term "laptop" suggests: it's comfortable on your legs, it's compact so it will go anywhere, and it gets good real-world battery life for light to medium duty (4 to 4.5 hours, roughly).
If you're going to do "heavy lifting," on the other hand, then you have to ask whether you want a full-on desktop replacement (like the Dell Inspiron 9300 or XPS) or whether you want a balance between speed and portability. Don't get a 17" screen if you're carrying this thing to and from class; you'd be better off with a 14" or 15" screen, and you should focus on something which is light while still having enough power to do what you want.
Also, if you go with Dell, either get an extended warranty or get the XPS model - not that they're overly prone to part failure, but you don't want to struggle with an Indian call centre any more than you have to.