Later today we will release the 4.52 RadEditor for MOSS update. I tested it and it on a local MOSS SP1 server and it covered the scenario you described. Here is what I had in the editor config file:
Notice that one path starts with a slash (because the Site Collection Images library is in the root site). The other path does not start with a slash, because the PublishingImages library should be loaded from the current site. If there is no PublishingImages in the current site, the image manager will not give you an error - instead you will see an empty folder with the name "not found". The other folders (in this case SiteCollectionImages) will load and work OK.
All the best,
the Telerik team