thecolclough, I don't think we can consider your advice on this matter particularly informative or helpful.
If you purchase a mac, imac, or macbook, then you should be prepared to learn how the new operating system and hardware work. It's different than using a mac on occasion in that it's yours and you paid for it; you'll be inclined to dedicate yourself to learning it without bias. Therefore you
will learn to get used to the differences and adapt. Things won't be "annoying", they'll just be done differently.
Judging from Apple's website, you'll get a one year repair coverage and 90 day support. This can be extended for a fee. As for returns, go here:
http://store.apple.com/Catalog/US/Images/salespolicies.html#topic-20 Seriously though, you should do your own research in this matter, and it's obvious you're not doing much of it. If anyone ever buys a new computer, they should know that research is the most important step in the process. If you ask individuals about it then you'll just get opinionated/biased information based on their personal experiences or what they think they observed about others' experiences, and you're just setting yourself up to blame others if you're not satisfied when you should blame yourself first. If anything, look up professional reviews and articles about the products you're interested in and what it takes to make the transition from pc to mac so that you'll be better prepared for it. You can also look at several customer reviews as a whole to get an overall impression of it.
And yes, you can run the Mac operating system on windows-based PCs. However, it's a complicated process for users without in-depth computer hardware/software experience. So do this at your own risk (my computer has windows xp, windows vista, and mac os x leopard on it).
As for what to get for either a windows or mac based pc, and what specs...again. Do your own research. You'll be more satisfied that way. For computer graphics, you should look at getting the best in memory, graphics hardware, and processing speed that you can within your budget. Don't overspend for outrageous next-gen hardware, because in a month or two you'll just look back and wonder why you paid so much for such a thing that you can't fully utilize.