You will find that it is a known problem at Mozilla.org.
This the German url for the description there will be en-US too i assume
http://plugindoc.mozdev.org/de-DE/important.html#shockwave
According to what i understand it seems easiest to install Netscape 4.8 and then the plugin. That gives other nice plugin collection anyway :-)
I will send You screenshots of there error to wanadoo.fr mail account.
This is macromedia error log in Macromedia profile
Tue Oct 10 17:57:38 2006: SwOnce...
Tue Oct 10 17:57:39 2006: sw: state is 0
Tue Oct 10 17:57:39 2006: Starting: 1014020, I:\DOKUME~1\ADMINI~1\LOKALE~1\Temp\GLJ4.tmp, , nt, 5.1
Tue Oct 10 17:57:39 2006: Shim version: 1014020
Tue Oct 10 17:57:39 2006: Do Switcheroo...
Tue Oct 10 17:57:39 2006: EnterUpdaterCriticalSection: 96, 0
Tue Oct 10 17:57:39 2006: sw: state set to 1
Tue Oct 10 17:57:39 2006: Didn't find I:\WINDOWS\System32\Macromed\update\New\Shockwave 10\swinit.exe
Tue Oct 10 17:57:39 2006: Didn't find I:\WINDOWS\System32\Macromed\update\New\Shockwave 10\swonce.dll
Tue Oct 10 17:57:39 2006: Warning: file I:\WINDOWS\System32\Macromed\Shockwave 10\xtras\QT3Asset.x32 is missing. Expected 1014020
Tue Oct 10 17:57:39 2006: sw: state set to 2
Tue Oct 10 17:57:39 2006: ExitUpdaterCriticalSection: 1
Tue Oct 10 17:58:33 2006: SwOnce...
Tue Oct 10 17:58:33 2006: sw: state is 2