You can add more than one item in the ImagesPaths list. This means that you can add a library from the current site as well. However, I am not sure that this will solve your problem.
The next editor release for MOSS will have an updated file browser content provider so you will be able to properly use libraries from all sites.
In the mean time, you can switch to the original MOSS image asset picker by changing the editor's tools file - change the tool "ImageManager" to "MOSSImageManager". However, you should note that the original MOSS image asset picker has known problems with the Firefox browser. Microsoft addressed these in the MOSS 2007 SP1 release, so if you have the service pack you should be OK.
the Telerik team