Is it possible?

Yes

What do you need to do?

lol, sorry, i don't know what you need, but i know you can

It's called dual booting, and yes I've seen it work. You can have both Vista and OS X on your computer.

You can install OSX on a Windows machine but I don't know how.
And it's not legal either, however it is to have Windows booted on a Mac.

Just get a Mac man.

Already purchased a Quad core Vista PC from Dell last week.
Just wanted OS X so that I can develop apps for the iPhone.

Borrow a friend/colleague/relative's Mac (if any)?

lol no, dual booting is not the same as running an os on another os. with dual boot you can only run one os at a time, its pretty much the same as switching HDD/partition at boot up.

as for the op, install vmware on your vista machine, you create a virtual machine which you can then install osx.

here is the examples, dont have time to give you details, plenty of links if you google.

http://wiki.osx86project.org/wiki/index.php/Vmware_how_to

yes vmware does run on vista, i have it running on vista 64.

really i dont understand why some of you guys use this forum for anything more than "why white men date asian women" thats all its good for

I misunderstood the question.

You can't literally install an Operating System on an Operating System without using software such as VMware, and even then it's not what you'd call installing an OS on an OS. I assume you mean the computer itself, yes you can. However I don't recommend moving to Macintosh unless you love watching graphical figures move around constantly. If you're moving to Macintosh for simplicity sake, then I understand why you haven't chosen Linux. If you're moving to Macintosh because it's more stable and prone to viruses, then I don't. Personally I have duel boot setup on my computer, Windows and Linux. The only reason I can ever see myself installing Macintosh for triple boot is if I was really desperate for the Iphone sdk, which I'm not. For starter's I'm going to have to recommend duel boot, I can almost guarantee you'll need to pop back into windows every now and then. Note that if you're doing duel boot, make sure you install Macintosh then Windows Vista(If using vista).

Mind you, I find Barok's comment quite racist. But hell, I'm new, I probably haven't seen anything yet.

jeez

your first 3 post mentioned something about racism already. did you join the forum to throw more fuel?

stick around you will get used to it

VMWare is very slow and it eats up alot of memory.

One of my PCs has quad boot (Ubuntu, Solaris, Mac OS X Leopard, Windows XP) I just use the GNU Grub.

yup using virtual pc is going to be slow, but its the only way you can run another os while the main os is running as per op original qs. best to boot the os directly from another hdd/partition.

You cannot install Mac OS X on ANY windows based machines, Dell HP etc... You can install Windows XP or Vista on a Mac though. Also you can run both OS's side by side with a program called Parallels for the Mac.

Brought a Mac Mini for iPhone development. Taking the Stanford University iPhone development course on the web.
http://www.stanford.edu/class/cs193p/cgi-bin/index.php