If you don't have a third party program for this have you tried the built in back up for Windows??  It is under Program Files/Accessories/System Tools.  Of course the easiest way is to know what you need to back, certainly not the entire HDD but items like My Documents, My Photos, etc and burn those folders to a CD before you re-load your system.  Hope this helps.

thanks, That is probably what I will do . Can you do  the desktop also ? to copy to a disk /

Yes you can.  That is located on the C drive in the following location:  C:/Documents and Settings/ /Desktop.  Just copy the whole folder then when you reload the system place the folder you backed up (or the contents of it) in the new folder (or replce the new with the old.  Simple.

Thanks