Do you have XP or Vista now?
I found some more info about installing it on same computer vs a new or different machine.

If XP you'll have to use a flash drive or CD/DVD to back up any files or settings that you want to save. it tells how to do that on the link.

plenty of pages to explore with clickable links to more info..

[Upgrade from Windows XP to Windows 7

The Upgrade option is not available in Windows 7 Setup when installing Windows 7 on a computer running Windows XP. However, you can use Windows Easy Transfer to migrate files and settings from Windows XP to Windows 7 on the same computer. To do this, you must first copy files to a removable media, such as an external hard drive or UFD, or to a network share. Next, you will install Windows 7 and then migrate your files back from the removable media onto your computer. When you are finished, you must install your software programs again, but your files and settings will have been copied from Windows XP.]

http://technet.microsoft.com/en-us/l...8WS.10%29.aspx