Question: I've read everywhere that you can't have more than 4 partitions because of GPT on intel Macs. But what happens if you make more than 4? On my iMac I have EFI, Macintosh HD, Windows, Linux, and Linux swap partitions and I am able to boot from all three operating systems with rEFIt. So, I have 5 partitions, so why does it work? I made the partitions with Snow Leopard's Disk Utility by the way.

Answer: 
I found [this article](http://www.rickycampbell.com/the-intel-mac-partitioning-system-efi-and-gpt/) which explains the partitioning scheme.

Essentially, if I understand the article correctly, there is an “Extended Boot Record” on one of the partitions on one of the primary four partitions which describes the extra "extended" partitions. Some legacy operating systems cannot see them.

Linux can see the extended partitions after the kernel is loaded. I presume you're able to boot properly because the Linux partition is on one of the four "primary" partitions.
The problem here is that, as cmurphy says, Windows (x64) can't use Apple's EFI implementation(which is basically EFI 1.1). It needs either UEFI (EFI 2.0) or BIOS. But because Windows has an [artificial limitation](http://www.rodsbooks.com/gdisk/booting.html) of tying up UEFI to GPT disks and BIOS to MBR disks, it needs some trickery to work. Specifically, Windows and OS X on an EFI 1.1 can coexist on a single drive "only" if Windows is fooled into thinking it's an MBR drive while it's actually GPT (OS X does not support MBR). This trickery is what is called Hybrid MBR - it's a dangerous and ugly hack like cmurphy says. 

However, you CAN boot windows on GPT from BIOS *IF* you have any *small* MBR drive you can boot off, or even a floppy. It's not even a hack and will even work on Windows 32-bit.

Basically Boot into the Windows install/repair disc. Just create the system drive on the floppy, and use `bcdboot` to put your boot files on the floppy. Add a bootsector with `bootsect`. Change the `{bootmgr}` `device` to `boot`. Boot from floppy.

Steps are detailed [here](http://www.sevenforums.com/installation-setup/320700-boot-windows-7-8-gpt-bios-system-no-hybrid-mbrs-duet.html).