Apple's bootcamp allows you to partition your existing Intel Mac hard drive and then install Windows on the second partition. You can access Windows by booting directly to that partition and running the machine as a PC or you can get virtualization software such as Parallels or VMware and access the partition through a Mac window and have access to both OSes.
It comes down to what you want to spend and how critical the tasks are. My needs are fairly low as I run a few legacy apps in XP and I just launch Parallels rather than rebooting.
So... if you just want to run windows, use bootcamp assistant (free in your application>utility folder) and have a licensed copy of your Windows OS (XP has to be service pack 2 or better I believe)