Stuart,
I recently bought a Dell Latitude D800 and am very happy with it. I considered buying an apple power book (the apple stores in the states are so cool its hard to walk out without picking up something) however a lot of the applications I might need for work (for example SAP) are not necessarily supported on an apple mac.
It really comes down to what you want the laptop for? Is it just for email, internet access, word? Or will it serve as a work laptop too? If so what type of appliations do you need to run? Are they drawing, design applications? Or company intranet applications (for examples sales tools such as emac)?
If you are looking for a laptop just to upload pictures, play music, movies, internet access, email, word then I would go for the Apple iBook (15" screen).
cas.