I will add comments to it in this post.
See if you have this file: C:\i386\explorer.exe and compare it's properties with the infected one. If you can tell they are different use this one to copy to the C:\ directory, if not copy C:\Program Files\Internet Explorer\iexplore.exe to C:\WINDOWS\
Rename the file you are going to use to Explorer.new
Preparing the good copy. Saving it as C:\Windows\explorer.new
Now open TaskManager by hitting Ctrl-Alt-Del
Open the command prompt f.e. by Start > Run > cmd
Divide to the two over your screen so you can work in both.
In taskmanager select all the explorer.exe processes and terminate them one by one.
Stopping explorer.exe so it can be replaced
At the first prompt type cd\
At the C:\> prompt type...
ren C:\WINDOWS\explorer.exe explorer.old press Enter.
disabling the infected C:\WINDOWS\explorer.exe
Now at the C:\> prompt type....
ren C:\windows\explorer.new explorer.exe press Enter.
Renaming the good copy so it will take over from the infected one
Now in Taskmanager on the Applications tab click "New Task"
and type C:\WINDOWS\explorer.exe
Starting the new clean copy
According to the Symantec site this one also gets replaced so we delete it
Hope that makes it a bit clearer.