1. latest DirectX version installed
2. latest Graphics card driver
3. search and change/add in \\Enemy Territory\etmain\profiles\ETUI\etconfig.cfg
if nothing will work:
try to rename (not delete, maybe you need to look about some old settings) your \\Enemy Territory\etmain\profiles\ETUI\etconfig.cfg and restart game.
new etconfig will be created and should work. (you have to switch all settings, since its running in lets say "safe mode")
ET doesn't use DirectX afaik. It uses OpenGL which are provided by GPU drivers. Dfighter what's your GPU? nvidia or AMD? Here is your error:
...WARNING: could not set the given mode (3)
So you should try r_mode according to your windows OS resolution.