It *might* not be in DX7 though
http://developer.nvidia.com/object/DX7_render_texture.html
Nice reading:
"Rendering to Texture Surfaces Using DirectX 7"
http://www.gamasutra.com/features/19991112/pallister_pfv.htm
Wrapping It Up
Being able to render to textures adds one more valuable tool to the developer's arsenal, offering many exciting possibilities for 3D applications and extending the range of available effects to new limits. Now that this capability is supported by a substantial installed hardware base, and the DirectX7 API exposes the feature, developers can start actively using it in their applications. We hope the techniques presented in this article will guide developers along the path to taking advantage of this approach to rendering.
By Kim Pallister
Gamasutra
November 12, 1999
Being able to render to textures adds one more valuable tool to the developer's arsenal, offering many exciting possibilities for 3D applications and extending the range of available effects to new limits. Now that this capability is supported by a substantial installed hardware base, and the DirectX7 API exposes the feature, developers can start actively using it in their applications. We hope the techniques presented in this article will guide developers along the path to taking advantage of this approach to rendering.
By Kim Pallister
Gamasutra
November 12, 1999
Since it's now 2004, I think that we can safely say that it would not be too "exotic" or "new" feature to add to Blitz3D... :)