How can I get the full software from any installed application?

Suppose I have already installed a software with my computer in any OS like Windows XP, Vista or Windows 7. The software disk is not held with me now. I need to format my computer. But, I wish to get back the whole software into a disk or in a hard disk to be extracted from the installed application. Is it possible? If so, how could I do this?|||Make a backup using norton ghost before you format. Restore from the backup after you're done. Norton ghost isn't free, but i'm sure you know how to get it.