Warning - My Brother did something like this on Vista and i had to reinstall the OS.
lot of themes packs are available...google it
Making a pc look like a MAC is much easier than making it work like a MAC. I'll assume you are seeking more than aesthetics...
Steven woodman is right, stardock has some products for this. Most all of them are really good too, but be forewarned that you will need extra processor and ram to devote to these application.
I have to say that running the window blinds and object dock both at once take a semi-powerful pc, and if you ever run across another Mac dock for the PC (I forget the brand, but it was not stardock) -- avoid it unless you have 16 gb of ram.
To make a long story short, you might consider buying a MAC instead of installing a handful of cpu intensive (& expensive) apps to hide the fact it is a PC :)
I did it on my computer,regret a lot,becouse it messet up up dll32,eventually it crashed and i couldnot uninstull properly.Not a big help,but i would not advice it...
specially the icons part... :) thanks
If you like a MAC that much, why don't you just buy a MAC,
Mac is more expensive than normal PC I think...
It seems that Stardock is ok, but errors happen sometimes.