As a long time Mac user I would vote for the Mac. The iBook is a sleek and fast little performer with long battery life.
Many PC users will talk about compatability and software etc but don't be put off by people who have followed the Microsoft Windows cult. All the popular packages are available for the Mac and you can save files in any format for PC users to open with their software.
I am now on my 6th Mac in 14 years and have never regretted it. My latest is the G4 and it is sooo fast. I use an older PowerBook for on the road but will seriously consider upgrading to the iBook soon (Xmas bonus permitting).
What the MS Windows brigade rave about, I was using on the Mac 14 years ago and has been developed and upgraded ever since. You won't find an easier computer for your work and to add software and peripherals is a doddle especially when compared to a PC running Windows. Just read the 'need help badly' thread!
Everything I create for PPRuNe is done on my Mac and then downloaded to a Unix server. Go for it.
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Capt PPRuNe
The Professional Pilots RUmour NEtwork
[This message has been edited by Capt PPRuNe (edited 01 November 1999).]