Version: (using KDE 4.4.1) Installed from: openSUSE RPMs The texture selection in the configuration dialog should allow to load custom background textures.
As a workaround, you can place your textures in the directory ~/.kde/share/apps/palapeli/backgrounds (replace .kde by .kde4 or similar if your distributor changes that), which is where Palapeli looks for its background textures. You will have to restart Palapeli to have it pick up the new textures.