MPEG-2 Explorer Thumbnails

(Note this is a copy of one I've posted into the Windows XP - General group,
but I'm putting it here too in case someone here can help)...

I think this topic has been discussed before, but this was some time ago, so
hopefully someone can help with this version of the problem.

I use a DVB-T card for Digital TV viewing on Windows XP Home SP2 (in the
UK). This creates recordings in an MPEG-2 (.MPG) file format. I have now
amassed a fairly large collection, which I tend to watch back in Windows
Media Player 11. Windows XP does not have an MPEG-2 Codec as standard, so I
have intervideo WinDVD 8 which provides the Codec for this.

The problem is that Windows will not Thumbnail these files in Explorer views
(all other supported video formats thumbnail OK). I believe that this problem
may be codec related, but fail to understand why Media Player can interpret a
Directshow codec and Explorer cannot.

I've tried the usual "regsvr32.exe shmedia.dll" and related fixes to no avail.
In fact, the only fix I've found is to install the "Elecard Mpeg2 codec" -
which enables explorer to generate thumbnails, the problem then is that this
codec then takes over from the Intervideo codec in Media Player, and the
playback quality is poor in comparison. I cannot find any way of forcing
Media Player to use a specific codec over others (Even Deccheck.exe won't
override this despite setting Intervideo as the preffered codec). I've also
tried a completely clean XP install to look at solutions to this, but to no
avail. I don't mind spending money on this if it fixes the problem.

Sorry if that is a little lengthy, I figure it's best to give as much info
as possible at the outset.

Anyone have any possible solutions, either to enable explorer to generate
these thumbnails, or to override settings in Media Players codec choice?
I class myself as a power-user and have no qualms about messing with the
registry etc.

Many Thanks

Damian C