Are you serious ? if yes then Below steps will help you .
1. Uninstall XP and install windows server 2003 or above,
May be you can put VMware on your XP machine and then create a Server as a VM inside it. (virtual BOX will work great if you dont want to pay for vmware)
2. Install Active directory somewhere, either on same server or another
3. Install exchange on it, You can get the setup ISO from MS website
Hope it helps