There is no such thing as a "for mac" version of Windows. If you want a copy of XP you'd better hurry up (if you can still get them at all - you may need to look on eBay). If you want Visturd, well, my sympathies.
Basically it goes like this:
Run boot camp wizard (in apps/utilities) to shrink Mac partition, leaving space for Windows.
Put Windows CD in and reboot.
Install Windows
Put Leopard disc in and install Windows drivers
Then whenever you boot, hold down the option key (alt) as you power on and it will give you a choice of which system to boot. You can also download a frankly more aesthetically pleasing and functional boot manager available called rEFIt, which is free but not essential.