I'm assuming that you start with either a XP or Vista. Within a hour, you will have a system that's running all 3 OS (XP, Vista and Leopard) and you will have a boot screen (an Vista boot screen) that let you choose which OS to boot.

If you want a real easy and problem free triple boot system, shell out a few bucks to get a separate hard drive for Leopard. From what I see, if you like the OS so much, that's the least respect you can show for it. It will save you countless hours of headache and your Leopard will roar much much happier. Sorry Laptop guys, this guide won't help you at this moment.

I'm a total noob, and I started off in this scene a few months ago when I experimented with Tiger. During the time I built a few systems using different hardware and experimented with different configurations. Now I'm running Leopard, Vista and XP on a Gigabyte P35-DS3L board which is a very common board. Best that you have a Intel CPU (duo core of some sort) to run Leopard smoothly. Nothing else really matters as I found that you can find a solution for everything.

OK, first, let's install Leopard:
1. Connect your new hard drive to any available port (SATA or IDE). Boot into your XP or Vista, use some sort of Partition software to partition the new harddrive into FAT32 and flag it bootable. You can use any partition software, such as partition magic or Gparted live CD. Doesn't matter. As long as it is one big primary partition of FAT32 and it is flagged as bootable.

2. Disconnect all other hard drive and only connect your new MAC (that's how I named it) drive and DVD Rom. Pop into your favorite Leopard installation DVD and start installation. I used iATKOS simply because I had good experience with uphuck's previous release.

3. Erase your MAC drive in Mac OS extended Journaled format in disk utility and go back to utility and install Darwin Bootloader. I'm not sure about other installation releases may have darwin bootloader integrated, but with the first iATKOS release, you need to manually install it from utility. Also, you may choose if you wish to install EFI emulation or not. If you wish to go with Stock(vanilla kernel) which promises more stability and speed (which I doubt but I installed anyway), you must install EFI emulation for easy future update (such as leopard 1.5.2... )

4. Now proceed to main installation. Choose only the main package, choose no driver or patch. You can always go back to add driver or patch. I found throug experience that less is often more. Wrong driver often gives you grey apple. Once you finished installation, reboot without the DVD disk in them. You should be able to boot into your new Leopard now. If you can't even see the grey apple, you either forgot to install Darwin bootloader or didn't flag your drive as bootable.

5. If you only see grey apple but either getting the restart or nothing, reboot into verbose mode (-v at boot screen) and see where you got stuck. Most likely it's the video card driver as Darwin will boot without sound card or lan card being functioning. But it won't boot into desktop if a video card driver of some sort can be used. Time to hunt for video card driver then. For X19xx series, use Jccool's package, for X88xx series, use nvinject (add your device id), for x8800 GT, use Leopard 1.5.2 GeForce kext package and openGL framework package. All can be found in this forum.

6. Let's proceed with triple boot process. You can always tweak your Leopard to perfection later on. Now Connect your window harddrive back to your motherboard. Go into bios and change the boot sequence to Window harddrive first as sometimes bios changed during the Leopard installation process.

If you already had a vista installed and don't want to install XP and are fine with dual boot with Leopard and vista, skip to step 10.

7.a. If you have only XP, now disconnect your Leopard harddrive from motherboard, you can either use a separate harddrive or you can create a new partition on the XP drive to install Vista.
7.b. If you have only Vista, same thing, disconnect your Leopard drive, install XP either on separation partition or totally separate hard drive.

8. If you had XP first and Vista after, your vista boot will be fine without fixing. If you had Vista first but installed XP later, you will need to pop in your Vista installation disk and do a repair and it will fix your vista boot.

9. Connect back your MAC drive and reboot into Vista. Once you boot up Vista, download the latest version of EasyBCD and install it on your Vista. Run it and check if you have already boot entry for both Vista and XP and have Vista as default. If you don't, add XP in your boot entry in "add/remove entries" section.

10. Ok, download and run EasyBCD if you haven't done so in step 9, in "add/remove entries" section, under "add an entry", click on Mac OS X, and choose generic x86 PC in platform, do not use auto configure setting, instead, manually set the the hard drive number and partition number. Here's how it is: if your MAC drive is plugged into the second (SATA or IDE) slot, pick hard drive number "1". And then pick partition number "1" as you only had one big partition for that drive remember? Click on "add entry" button and close EASYBCD.

Reboot and you will see a nice triple boot option and test to make sure all 3 can boot up respectively.

Notes: if you are using a mother board with Intel ICH9 chipset, unless you patched the kext, your Leopard will not be able to see the Last 2 SATA ports, very important. To solve this problem, you either patch the kext for Intel ICH9 or never ever ever put your MAC drive on the last two SATA port. You may put any other drive on the last two port (namely vista or XP).

That's it. Post your question here and I may have left out some info. I'm very new to guide writing and I'm kinda lazy. You have to hunt all the patches and drivers in this forum as everyone's system is different.