To answer the OP:
Halo 2 Vista will run on your Mac as long as you use Bootcamp to install Windows Vista or Windows 7 first. I don't recommend the other vitalization software for gaming.
Is it worth it? In my opinion, no. As Dusk pointed out to you very legitimately, Halo 2 Vista is a BAD PIECE OF SOFTWARE. This is not my opinion of the game, or those who play it, it's my opinion of the software itself. The code. It was not "ported" well from the Xbox, in fact Halo 1 for Mac/PC and Halo Custom Edition are much better when it comes to software. Not to mention that Halo Custom Edition is much more open and has more potential for customization than Halo 2 Vista. Out of the box the only thing you can create "custom" in Halo 2 Vista is the actual maps. Vehicles, player bipeds, weapons, etc is all restricted...
Bottom line - Halo 2 Vista is a bad implementation of a good idea. Save your money and Stay away.
On another note:
I recently working in an Apple store as a Genius, I quit because most of the "technical support" that I was given from the other staff wasn't "technical" at all. 90% of the problems really didn't require the other associates to refer the customer to me, those associates should have been able to diagnose the problem verbally and provide instruction.
I say this because 90% of the time when a customer was sent to me to have a Mac "fixed" it was just because they had improperly used the software and couldn't figure out what to do... From my experience, this speaks loads to the type of people who buy Macs, however I'm positive that there are those Mac owners out there that know their systems inside and out.
I had similar cases while working as a PC Technician at a local computer parts wholesaler but the problems were generally "technical" if they got to me, meaning hardware or complicated configuration within Windows.
When I was working at the Apple store I was given 100% leniency when it came to recommending other products from other manufactures. When working a normal shift at the store I regularly convinced customers very easily that the 2X price for a Mac was NOT worth, especially when I was able to recommend software alternatives almost every time. For example, someone comes in wanting to use Garage Band and I was able to listen to their needs and provide them with a better alternative that would work on a PC.
I'm sure it helped that I recommended Newegg and always had a small brochure of my own on hand recommending video and text tutorials on building your own PC. This generally saved my customers $500 or more on the PC which they were able to put towards better software then what was available on the Mac. I also included some of my personal contact information in those brochures to make sure the customer could call me if they had any questions. I even made a FaceTime call to one of them once (iPhone to iPhone of course) to assist him with a question he had while installing his custom heatsink onto his motherboard.
I must say that the 12 or so customers that I recommended PC's to have commended me to the Apple store staff, who in turn increased my pay before I quit (hah). Anyhow, I keep in contact with these customers in case they ever have problems. Most of them are much happier that they bought a PC, the rest are indifferent but appreciate the money I saved them.
My point here is that I'm more than qualified to tell you which I think is better than the other. In most situations I have to recommend a PC unless you're completely reluctant to learn what I like to call the "PC Basics". If you're not willing to learn how to diagnose small problems you're having on a PC before calling for support them a Mac is probably for you. Overall they seem to have less software and hardware problems, but their users don't know the first thing about self-diagnosis so they run to the Apple Store and seek out a Genius to do it for them instead of learning... I honestly don't need to deal with those kind of people.
PC's are cheaper, faster (for your money), and much more upgradable than Mac's. If you're a power user or hardware enthusiast your only option is a PC. If you're a gamer, you can go with Mac if you want to support the brand, but you're going to be forced to use Bootcamp and suffer worse performance than the same hardware would give you on a PC. Is that worth it to you? If it is, by all means buy yourself a Mac. I'll stick to a PC for all my computing needs and save myself tens of thousands of dollars. Literally. The PC's I generally build for myself are in the $5,000 range and include water cooling, water cooling a Mac is hardly an option at this point...
[Edited on 04.08.2011 10:06 PM PDT]