I was wondering how cool it be if it is possible for a desktop computer to be capable to have Microsofts Windows 7 and Apple IOS snow leopard or higher.Just throwing this idea out there but it might have been done already. 
The dell mini 10 and dell inspiron 1525 and 1545 all will run mac osx snow leopard and maybe some others.
just search the internet for guides on how to do it.
Look up bootcamp, it will allow you to run windows on a mac device.
Its usually called dual-boot or multi-boot.
You can install GRUB to the master boot record and repartition the drive or add a new drive on which you install snow lepoard. If you are doing this on a Mac you could repartition and install GRUB to the MBR AFTER installing windows to the new partition.
You can do this but I suggest you do a little research because it matters which OS is installed first.
I have a dual boot Linux/ Windows XP Dell inspiron 1525. I found the info I needed on the internet. I did this because I was starting my Linux Admin Class at ITT Tech and was given the same warning about researching it.
The main issue is the fact that windows always rewrites the MBR. It may be easier to just use VirtualBox which is a free emulator, which will effectivly allow you to run an OS inside of another OS. It would most likely be easiest to make 3 partitions and use Linux Windows and Mac installing Linux last as it will write the MBR with GRUB which can autodetect the other OSs.
A lot of Mac owners have WIndows on dual-boot.
I just save the time and use Windows. Oh snap.
I use Linux all the time, and if i need to run windows programs I just use wine, but usually I dont need to as Linux has opensource versions of almost everything!
1. It's already been done, and another Revision3 show Tekzilla did a video on it a while ago; 2. It's highly illegal and unethical, plus extremely hard to pull off because of the home made drivers out there aren't always 100% in working order.
yes it has been done many times on the internet. No its not illlegal unless you use a cracked version of either Windows or IOS and then dual boot system is not illegal only the cracked version of the software.
Another way of doing a dual boot is to make a virtual operating system also.
Make sure your hardware is compatable to each OS and if you google "windows 7 and mac leopard dual boot tutorial" without the quotations you will find a lot of examples.