Your description indicates that you installed a new copy of Windows in the same partition that your original XP was installed in. Now you can see your programs in c/Program Files, but they are not "installed" in your new XP.
Save all the files you want to keep by burning to DVD or CD as your system may be capable of doing, or to another hard drive. Re-install Windows and this time have setup format the drive (quick format if you have no drive issues) and then re-install all your programs. Later you can copy back all your files you saved before the format and new XP installation.
You cannot save programs from C/Program Files and expect them to work again if copied back to your new install.
Only your data files are salvageable. Programs must be installed by the vendors installation methods.