Capt. Chambo:
If there's only one application you need to run under Windows, you might be better off getting the Parallels emulator –*unless it's a graphics-intense application, it should work well enough without too much loss of performance. With an emulator, you don't need to reboot back into OS X.
Microsoft haven't supported Messenger on the Mac for ages, but you can get audio and video capability on MSN by downloading
aMSN for free.
I've been using Macs for 19 years and never had a virus, worm or any other nasties. I regularly receive DOS attacks on my internet connection, which continues to work with my Macs unpeturbed. You can turn on the software firewall, but (at the moment), it's not really necessary, especially if you're behind a hardware firewall (usually built into your router or modem).
I agree – dotmac accounts are great! Logbooks all backed up!