Arshad, so would I want to get the M of 4?
Sorry, I should have made that more clear. From a pure power consumption and "work per watt" perspective, you want to get a Pentium "M", which has a different architecture than either the "Pentium4 M" or "Pentium3 M" (even though it's largely based on the P3 architecture). What this generally translates to is a laptop with longer battery life, and one that weighs less since you don't have to stick as large or as many batteries in.
HOWEVER, they also charge a premium for the PentiumM, and the overall performance is not necessarily better than a P4 or Celeron based machine since they are typically clocked a lot higher. eg. a 2.8Ghz P4 vs a 1.2Ghz PentiumM or whatever.
The key thing to remember here is that you Mhz is not apples to apples. The architecture defines how efficient the chip is per clock (Mhz is essentially a million clocks per second). A pentiumM at 1.2Ghz is going to have higher performance for the most part than let's say a Celeron at 1.8Ghz, but a 4Ghz P4 is still going to smoke that PentiumM by sheer clock speed.
I know, it's all very confusing! Just keep in mind, that unless it specifically says "Centrino" or "PentiumM", it's not. If weight and battery life are not as big a concern, I would just go with the much cheaper Celeron or P4 based laptops.
Personally, I never really understood the appeal of MacOS unless you are a graphics guy - but that's just me.
You know that's a common misconception. Back in the day, all of the graphically intensive applications were only available on the Mac, like Photoshop and Illustrator and Quark etc. Now, you can get all of them on a PC and until the G5's came out, they were more responsive on a PC! From a pure "graphics" perspective, at one time there were HW accelerators for the Mac when the PC was still using non-accelerated VGA, but these days the performance is somewhat higher on the PC than it is on the Mac, often even with the exact same graphics chip. Trust me on this one, I work for a company that provides PC's and Mac's with their graphics chips, and I personally work on the graphics chip drivers for Apple machines. Macs no longer have any advantage in graphics, either from a HW perspective or from a SW one.
Having said that, there are more reasons than ever to be using a Mac than a PC. Nowadays the excuse that "It doesn't have the software I need" is largely not true since pretty much all the popular SW is available on the Mac as well. Even the top-tier game titles all make it to the Mac. It works perfectly fine in a plug-and-play fashion in most corporate environments with the email system, with the network, etc. The advantages come from a much better user experierence, much easier setup for things like networking, and tons of very easy to use built-in applications for the home user, like iDVD, iMovie, etc. On my PC, I am constantly barraged by security updates from MS to avoid the latest virus/worm, I have to worry about which email attachments I can open, which files someone else using my machine might download, and am constantly being hit by spyware which bogs the machine down. This is now a very big deal for me because it interrupts my workflow on a regular basis. On the Mac, this is a nonexistant problem. These days, that's the biggest reason for me to be using a Mac instead of a PC.
Looking into the future, the next major release of OSX has a VERY cool feature which is their advanced searching. It's very hard to describe in words. When I first read about I was like "ho hum, big deal", but after seeing it in action the first thing I did was install "Tiger" even though it's still in early alpha stages and has plenty of other development issues, simply because of how powerful this feature is. (Since we work so closely with Apple, we get all the development builds pretty much from day 1). It's one of those things that are truly going to redefine HOW you use the computer! The biggest issue for users these days is information and data management. Hard Drives are getting huge and people have thousands of files and bits of information which are scattered all over the place. Even if you are meticulous with your organization, it can be difficult to isolate a particular bit of information -- you know you read it somewhere, but which file or email was it in? Tiger solves this in an elegant manner -- it truly is a paradigm shift in how you use the computer, and when my longtime hardcore PC/Mac-bashing friend saw it in action he was so convinced of how awesome it was, he just went out and bought a Mac laptop a few weeks ago ;-) Anyways, this is totally off-topic and I apologize... back to the original topic!