I work for a newspaper in the IT department and we use both Macs and PCs. Here's my $0.02 on what questions you need to ask yourself before you replace your laptop.
Other then Powerpoint, do you have any other applications that you currently use on your PC that you would like to use on a Mac?
If so, is the application available on the Mac and does it use the exact same file format as your PC version? In earlier releases of MS Office the Mac version would be 6 months+ behind the Windows release and this causes some headaches whenever Microsoft changed the file format.
Does the Mac version of the program you currently use offer the same feature set that you current use on the PC? Again, I've seen this a lot with Microsoft and a couple of other vendors where the Mac version may be missing a feature that the PC version has. This is only important if you use that particular feature. I use MS Outlook on the PC and need the ability to assign tasks to people, that feature is not available on MS Outlook on the Mac. BTW, the Mac version of Outlook will only work if you connect to an Exchange server and can either run OS 9 or classic mode in OS X.
If there is not a Mac version available of your current program, can you find a substitute program that can read your existing data? I've found some great substitute programs for a number of applications that I think work just as good as the programs that I would normally use under Windows, but if you cann't read your existing files a substitute doesn't do any good, unless of course you don't mind recreating all of your files.
What is the cost involved in replacing the applications for use on a Mac? You may still qualify for upgrade pricing, in other cases you may have to buy the full version which is more expensive.
Are there any programs may want to run on the laptop in the future that are only available on one platform or the other?
Have you used Mac OS X? It is nothing like OS 9 and eariler. If you have used it do you like using it?
Under OS X, it is less likely your computer would get infected with viruses or spyware but still possible.
Virtual PC is an option if you need to run Windows programs on a Mac but be warned it is very slow. I just installed Virtual PC 7 on a dual processor 2.5Ghz G5 with 2GB of ram, and well I think my 4 year old PIII 600 at home ran programs faster.
It is hard to find a laptop anymore on either platform that does not come with or offer wireless networking (802.11 b/g aka Apple Airport), wired networking (usually a 10/100 NIC card if not 10/100/1000), a 56kbps modem built into the laptop.
Most USB devices I've found are Mac compatible, usually via Apple's built in drives or from the manufacturer.
I still think Macs need much more ram then Windows does to perform well. I wouldn't recommend running OS X with less then 512MB of ram, and for most applications under Windows 512MB is more then enough.
The 12" Powerbook will come with a Firewire port, so you could connect a Firewire device to it. This may or may not be offered as an option on a PC.
The 12" Powerbooks only offer a MiniDVI video out, so you would need an MiniDVI to VGA adapter to connect the laptop to a projector. Most Windows laptops still have VGA video out.
The Powerbooks just have a touchpad for the mouse. On a Windows laptop the pointing device can vary by manufacturer, you can have a touchpad, the "eraser" style, or Dell gives you both.
After all of that since you are going to be taking it on the road the laptop needs to be reliable. I would suggest checking out
PC Magazine's 17th Annual Reader Satification Survey.
After all of that, which one would I go with? I'd go with what ever one was cheaper for me after I added in the cost of software, hardware, and any tweaking (adding extra ram, adapters, etc), I wanted to do to the system.