aspekx: This is what I get. The message screen unfortunately doesn't appear to be movable. I attempted to move it by grabbing the top of the message window along with the sides. If I am missing a way to do this please let me know.
The search I entered was "dungeons and dragons".
The ampersand (&) is the important bit you're missing. It won't do that much good, though, since "dungeons & dragons" still returns a bunch of irrelevant results that include not only games that include either "dungeons" OR "dragons" in the title, developer or publisher, but games whose title or dev/pub name contains words their algorithm considers similar to those strings (usually off by one letter). It's...not helpful.
Also, not all D&D games have "Dungeons & Dragons" (or variants thereof) in their titles. I used to have a bookmarked set of search results that displayed all licensed D&D titles that are on GOG at once, without any non-D&D results, but there's no way to make that work using the new search engine. I would recommend searching:
"hasbro" (publisher of some of the '00s-era D&D titles, and nothing else here);
"beamdog" (developer/publisher of the enhanced editions of most of the Infinity-Engine titles, plus the 2002
Neverwinter Nights, and little else here);
"sneg" (the publisher that took over publishing of most of the old games previously published by GOG themselves, including a bunch of originally-SSI-published D&D classics); and
"baldur" (just to catch a couple of titles not covered by any other search term). those four searches should get you all the officially licensed D&D games that are sold here, with as few overlapping or extraneous results as possible.
This, of course, ignores a number of "D&D in all but name" games that are sold here. :)