where Win7 is already installed? I would like to install xp because most of the softwares that i've been using have problems with win7. How about the drivers for the hardware, will there be a problem?
1) at the other partition on hdd, not the same windows 7 is installed (you have to create the other partition on hdd). how to setup dual boot installation windows 7 and windows xp look here:
http://www.sevenforums.com/tutorials/8057-dual-boot-installation-windows-7-xp.html
2) by clean install windows xp sp3 and formatting hdd (you lose windows 7 permanently).
but, if your windows 7 is professional or ultimate edition (not starter or home edition) you can run that software in compatibility mode; right-click at run icon of software, choose properties, open compatibility tab and set compatibility mode to windows xp (sp3), click apply and ok.