Erm, copyright infringement means you made a copy of something that isn't yours. That's what it's called COPYright. When you buy OSX you have not made a copy, so you're not infringing copyright law. You're breaking the EULA, your contract to legally USE the service. In this case, the software. That's a different thing. Also interesting is that EULA's have never been tested in court!
1. When you hand over money and receive a box with MacOS X 10.6, you haven't bought anything yet - the sale is subject to your acceptance of the license. You can refuse to accept the license and return the software and get your money back, or accept the license and the purchase of a box is now final, or do nothing and hold a box that you don't own.
2. No copying and therefore no possible copyright infringement happens until you copy the software, for example by installing it. If at that point you haven't accepted the license, then you don't own the box, so _any_ copying is copyright infringement.
3. Assuming that you accepted the license terms, then installing on a non-Apple labeled computer is in breach of the license (so yes, you are right, there has been a breach of the license), but you also committed copyright infringement. And the license that you accepted also states that you lose all rights to use the software if you breach the license, so booting that computer, which copies part of the software into RAM, is also copyright infringement.
Let's take some hypothetical cases to make things more clear: I sell you some software that I have written and the license states "You agree not to wear green jumpers while using the software". Wearing a green jumper is a perfectly legal thing to do, so doing this while using the software would be a breach of the license and nothing else, while copying software in breach of the license is both a breach of the license and copyright infringement.
Another hypothetical. The license states "you may install the software on one computer at a time only; if you install it on two computers you pay me $10,000". In that case you could always claim you never accepted the license, in which case making two copies would be two copyright infringements instead of one copyright infringement, one breach of license, and one payment of $10,000.
And EULAs haven't been tested in court? Google for "ProCD vs. Zeidenberg".
For a contract to be binding both parties have to agree upon it. You cannot enforce a contract on someone. I can purchase Mac OS X and not agree to any contract. So the law can't say squat. The only way to rectify that is to make sure someone agrees to the contract before the sale is final. But that is not how software is sold. When I buy software on Amazon, before reading any "hidden contracts" all sales are final. That's not a contract so far as I am concerned. Nice try to bully your point across though.
The law doesn't really care what misconceptions you have. Your misconception is that by handing over your money you entered a sales contract and then the seller springs some additional terms in you in the form of the EULA. That is not what happens, at least not in the case of MacOS X. Apple offers to sell a copy of MacOS X, but the offer is conditional on your acceptance of the license. Handing over the money is not enough; the sale only has happened after you accept the license. You can refuse to accept the license and ask for your money back. Obviously by handing over your money and getting a box (with no final sale yet) you are not agreeing to and not bound by the license, but until you accept it, the deal isn't done, the box with MacOS X inside is not legally yours, and _any_ copying would be copyright infringement.
BTW. The license is not "hidden". It is very visible when you try to install the software. It doesn't have to be visible to you when you hand over the money, as long as Apple accepts the software back after you find the license.