If you still have the SP3 file and its name is windowsxp-kb936929-sp3-x86-enu.exe, then create a folder in the root of C: and name it sp3, then execute the following command: windowsxp-kb936929-sp3-x86-enu.exe -x:c:\sp3
When finished extracting, there should exist c:\sp3\i386 containing the extracted files. Now you should be able to use Add/Remove Programs, Windows Components to add IIS and point it to that i386 folder. (If you have another i386 folder in the root of C:, you
may want to get rid of it (unless its an SP3 i386, in which case you can install IIS from it)).