You will now need to put the original Morrowind CD back in your CD bay, or the game won’t launch. Start the game, to ensure that it all launches. You just need to get as far as the main logo/options screen (as seen above).
Now might be a good time to install the latest graphics drivers for your graphics card (but don’t then use the Nvidia Control Panel to tweak Morrowind’s graphics – only the Morrowind Graphics Extender can do that).
If you run on 64-bit Windows, you may also want to look at the 4Gb memory patch. However, note that Morrowind is more CPU-intensive than anything else.