Hi Nick Once you know the Model # of the laptop and the linux distro you will be using. Spend time searching Google and Google/groups you will learn from others. I just did a search for "Acer travelmate linux" and saw good and bad experiences.
Laptop hardware is less and less a problem on Linux, but there are some very good resources out there for picking laptops and listing individual peoples' experience with installation on various models. The first one that comes to mind is [linux-laptop.net ].
I don't have any greatly useful personal experience to add, though. Debian runs great on my 1992 IBM ThinkPad (i486, 4mb, 160mb, 7.25in 8-bit greyscale screen), but you're presumably looking for a laptop choice with more processing power than a modern PDA ;)