Just got Houdini Apprentice installed last week. I got it to run once. Now it seems to open but is a transparent window. I can still see the desktop as well as the title bar for Houdini but nothing else.

Running an Athlon 64 w/ 1 Gig RAM, GeForce 6800 (77.72 drivers) on Windows 2000 w/ SP4.

Anyone have any ideas?

You have a graphics card issue either with the card itself not supporting OpenGL fully or your graphics driver.
Do a search on the forum to get more info.

This has been covered many times in the past.