I have to work on Apple Macs a lot of the time (when I train people on Photoshop, Illustrator etc) because they tend to be popular in the advertising industry and other media-based businesses, so I have a lot of experience of them, even have a couple of Macs in my house, including the massively overpriced Macbook Pro thingy which my missus insisted on buying:rotfl: So I know a fair bit about them, and what to watch out for.
The new (Leopard) operating system, which you will likely end up with if you buy a new Mac has a few problems. In a bizarre twist of insanity, Microsoft tried to make Vista look like Mac OSX, while Apple tried to make Leopard work more like Windows. Pedictably, both Microsoft and Apple have copped a lot of flak for these moves, but more importantly for you, the new Leopard O/S does now introduce something we PC users have been used to for quite a number of years to the Mac fraternity, the 'blue screen of death' or more correctly, it's a bit unstable. In fairness, Apple have patched this, but it is not totally sorted.
You might also want to note that with the switch to Macs using the Intel processor these days, and the newer operating system, Macs are not now the happy 'everything works on a Mac' software paradise they used to be, and to some extent this has been true since they went to OSX (the one before Leopard), so you find things like Adobe Illustrator CS2 crashing on OSX on an Intel processor Mac if you have the attributes palette open (which is not very helpful). Other pre-CS3 applications are similarly unstable on Intel-based Macs, which is a bit of a bummer since Adobe Acrobat 7 (i.e the CS2 variant) is far better than Acrobat 8 (the CS3 version), which is, to put it bluntly, a big pile of arse.
But to answer your question about extras you might need, in theory you shouldn't need anything too expensive to emulate a PC environment, but be prepared to ditch much of the standard Mac stuff in order to do stuff on the Internet, as there is little support for Mac stuff on many sites. An example of this is the fact that I had to ditch Entourage the crappy email software from my wife's Macbook in order to get it to pick up mail and connect reliably to my (PC-based) wireless network at home, so she now uses Mozilla's Thunderbird for email on her Mac for example. But what is more of a bummer for Mac users, is the fact that (like Vista) you can often find yourself unable to view things on websites because they don't support Mac stuff, a big example of this is the BBC's 'watch again service' which supports neither Vista, OSX or Leopard for that matter, whereas if you have Windows XP, you're in business.
My wife Max has just read this over my shoulder and she thinks PCs are the spawn of Satan, and Macs were created in heaven by the little baby Jesus, however, she just read this message and does not disagree with its content. But she still perseveres with Macs and, like many people, will always love Macs no matter what I say about them.
One last thing, if you are used to ripping out a graphics card and slinging another one in your PC, or RAM or any other bit, be prepared for a shock. In order to keep your Mac under warranty, you will have to use Apple Authorised components in it, and Apple authorised usually translates as Two years behind PC in terms of development and four times the price of the one you could buy for a PC that doesn't have the Apple Authorised sticker on the box.
Got to go, my wife has commanded me to make a brew as punishment for daring to slag off the Mac.

Chock