Two problems
1) media player problem download tracker-cfg then open it from app menu Then go to watches tab in there look for no watch directory then add the folder where the files are located which you dont want media player to show. Save the settings By clicking on the top menu then click on rebuild database on the top menu and done.
2) gallery problem go to file manager create new folder call it "private" under default n900/MyDocs folder copy and paste files and folders you dont want gallery to show.
hope this helps