John,
I must add : I have 24 Gb of Ram on a 2,66 Ghz Mac Pro Quadcore Nehalem
Thanks for the screenshots. It looks like to me that you have Spotlight indexing PM's cache folder. Looking at the file size of the image in the preview (448KB), I would expect it to be pixelated.
You'll need to force Spotlight to not index your PM Cache folder. Check PM's Caching preferences. If you have chosen a Disk Cache folder other than the default then you'll have to tell Spotlight not to index that folder. You can do this by opening up System Preferences, clicking on Spotlight, then clicking on the Privacy tab. Then add the same path you chose for your Disk Cache folder.
This should stop Spotlight from returning results from PM's Cache folder.
-Kirk