OK this is probably a silly question, but if you are using FreePascal, why are you using dglOpenGL as your OpenGL interface? dglOpenGL and most demos from Sulaco's site are specifically built for the Delphi compiler. So in order to get it working with FreePascal will take a fair bit of jiggery pokery.

IIRC, FreePascal has it's own set of OpenGL headers. Replace dglOpenGL in your uses clause with, gl, glu and you also need glext in there as well. This change should take place in both your project file and in the texture.pas file. The project will need a few more tweaks before it works. One main issue is that Textures.pas uses the Delphi Graphics unit. You will need to find out which FreePascal unit is its equivalent before proceeding.

Actually I just checked and FreePascal comes with a few OpenGL GLUT based Pascal demos.