Wow! Great price on the PowerBook. That does make it more appealing.
The Intel integrated graphics is fine for general email, browsing, and office applications. It may handle some basic 3D gaming, but if you plan on gaming with it, you'll be disappointed. The nVidia graphic are much more capable, and wins hands down.
As far as email, you can get Office for Apple, or consider Thunderbird
. I'm not familiar with the capabilities of AppleMail.
OSX is a terrific operating system. In many ways it's already what the next generation of Windows (Longhorn) hopes to become. Apple systems have VERY few problems with viruses, trojans, spyware, and other malware. It is a secure operating system, but lack of market share probably has more to do with it than anything. There's supposed to be an announcement about Apple changing to Intel processors sometime today, that may increase their market share -- and maybe you'll be able to soon purchase an PowerBook with a PentiumM.
PowerBooks do have better quality and build than a Dell Inspiron line notebook. Latitudes have great quality, but a much higher price tag. PowerBooks are also sexier.
Unless you already own a lot of applications for a PC, or have a need for a specific program that may not run on a Mac, I would feel very confident recommending the PowerBook over the 700m, if they were about equal price.
P.S. I do not own an Apple, but just last week ordered a MacMini. I decided it's time to experience it first-hand, and learn more about them. OSX is a terrific operating system, and I'm also intrigued about the ease of which it can run Linux aps.