I would need some more clarification before I assist you with this problem. I would like to know the type of installation you want to make. Are you trying to Upgrade your computer from Windows XP i.e., you want to preserve your programs, files, or settings? Or, you want to do a Clean Installation which will not preserve your programs, files, or settings. I would also like to know the type of media you are using to install Windows 7 (i.e., you have a DVD for windows 7 or a USB pen drive with Windows Image or any other media).
Further, it would be of great help if you could mention the System's Configuration (i.e., RAM, Hard Drive, Processor, etc.)