L337,
The Mac vs PC debate has being going on for decades. The main difference is that Apple produce both hardware and software, whereas Microsoft try to cover all the bases in terms of hardware and have ended up with a (still) DOS-based system which essentially has to be all things to all men; it will always be a compromise as a result. Apple have complete control over the hardware-software combination and can ensure operability in a way that Microsoft continues to find a challenge. Add to this the fact that the software is more intuitive to use, there's no need for antivirus software, and that Apple system updates actually become leaner and faster through its development, and you have a computer which is made as much as possible to have the maximum resources available to the user.
The iMac will more than do the job you describe. iMacs are used all the way from simple word processing to architectural 3D design. The Mac Pro is really more specialist for those who need ultra-fast rendering for their video projects, for example, where uber-performance really matters. However, in 9/10 cases, the iMac will be more than capable. Many web design businesses use iMacs because they are very powerful and look great at the same time. They will be running Photoshop, Dreamweaver, Xpress, Final Cut Studio, Logic.
If you get a Mac Pro, you don't need to use an Apple monitor.
Applemacster.