I can't speak for particular systems, as I don't know what you'll be able to get in that Oz place you live in (Why is that country so far away, anyway? What the hell?), but I'll address some generalities:
Dell was once good. Right now I associate them with late-90s Packard-Bell, who wanted to make the cheapest machines possible, and it showed. Dell sources its parts based on price and price alone. I've also observed many of their laptops to fail completely after about the two year mark. I don't plan on buying another laptop from them.
HP computers don't seem to be noticeably worse than Dell computers, and their service is superior.
Sony Vaios are beautiful little machines, but almost as overpriced as Macs. I have less data on them, but my Vaio that replaced the Dell is still running.
As far as video cards, in general the desktop version will run faster because they're looser on the power and heat restrictions. On the other hand, the mobile versions are almost always later revisions of the same chip, and thus have had some time to mature. This means that a mobile 7600 (or whatever) will most likely run slower than a 7600GTXOMGPWNT card you'd put in a desktop, but will have the same features available and will likely have fewer glitches. Usually if you do some digging you can find the important stuff like processor speed, memory speed, and number of pipelines, and then compare them to the desktop version. Most often the laptop version equates to the "budget" card for a particular chip in a desktop.
Something unfortunate to be aware of, though, is the fact that laptop video drivers are updated much more slowly than those for desktops, if they are updated at all. When I last looked into it there was a way to hack desktop drivers to work on mobile chips, but they weren't universially successful. If you play games with release notes that say "We need version 26.92r581b or better to work correctly," you might run into problems with a laptop. If you play older games this will be less of a problem.
I don't have to say to get the newest video card with the most memory you can possibly afford, right? 'cause they can't be upgraded, right?