Well in fact very strange :-)
Deleting or copying over the existing file doesn't work.
I'm using 4NT and did this:
move shell32.dll shell32.dll.orig
xcopy SP3location\shell32.dll shell32.dll

After the move the shell32.dll file still exists but is overwritable ;-)
just check out the size of the files before and after the action
Strange stuff but it worked for me.

If this doesn't work, maybe boot windows with only the command prompt...