most games offer a choice so the user can experiment
This is exactly what I'm doing... but I want to either "grey out" or disable the option for hi-res textures "automatically", transparent to user. That would seem IMO bit more professional than pop-up text saying "please try this and if you think that you are really getting hi-res textures then your card probably has them - proudly coded with Blitz3D" :)
Can't you create a texture of any size and then check its Width and height to see if it was created properly?
Yes, but that was just one example. DX Caps can give you *a lot* of (3D) system information, so general command for getting *any* Caps info I want would be good.