PPRuNe Forums - Windows Installer

I have used search - promise. The only thing close is Blue Eagle's problems in 2004 and they are not exactly the same. Trying to start Windows Installer ( XP with SP2) I get the message : Error3 : The system cannot find the path specified. This path being C:\DOCUME 1\user\LOCALS 1\Temp\IXP000.TMP. There's a couple of squiggles as well which I cannot reproduce. Thinking out of the box - had a look at my Laptop ( XP,SP2) which DOES start Windows Installer BUT from C:\WINDOWS\System32\MSIExec.exe/v which seems a sight more sensible. Just for the sake of argument tried my EFB Tablet runs ( W2K) which is slightly different - C:|WINNT\System32\MsiExec.exe/v. Still makes sense though.
Am I right in thinking that somehow the executable ( .exe) file on my PC has been corrupted and replaced with the .tmp file? And that to get it back I shall have to go into the registry after backing it up and creating a restore point? Or am I missing something? MS Product Support were all that you would expect them to be.
Thanks in advance...Soddit