Brian

It should import any attachment in that forum no matter what the extension is. If you need to get rid of some afterwards though then you should be able to run a query like this:

DELETE FROM adv_gallery_images WHERE extension = 'txt';

Then after you remove any extensions you don't want in there, run the 'Scan Database' option in the maintenance section, as well as the 'Update Counters' option and that should take care of everything.