Mike,
1. Insert the Windows XP CD
2. Click [Start] [Run]
3. Type the following command and press Enter
"rundll32.exe advpack.dll,LaunchINFSection C:\Windows\Inf\sr.inf"
System Restore core files should be reinstalled. Also, make sure the System Restore service is ON.
Alternately, you may also open Windows Explorer, navigate to "C:\Windows\Inf" folder and right-click sr.inf (choose Install)