To Run SFC....

Start - Run - (type)sfc /scannow

A small DOS type screen will briefly appear and then disappear. (this is normal)
Then the Windows File Protection "progress bar" will appear and track the progress of SFC.

If SFC identifies a missing or corrupt file (hopefully it will notice C:/WINDOWS/System32/MSHTML.hlp.file) then it will prompt you to insert your XP installation CD so that it can copy and replace the file.