Is there any way I can use a DDraw function to texture a given area (a RECT) with a current surface, or do I have to write code that tiles the surface within the RECT while applying appropriate clipping myself?

The Blt functions should do the trick.

Helpful links:
How To Ask Questions The Smart Way | Google can help with your question | Search MSDN for help with standard C or Windows functions

I know how to use the Blt function... but I was wondering if I could take a surface and TEXTURE it onto another surface within a RECT or something. Not just blit the surface, but texture it like tiles. I have code that does this, but if theres a DirectX function that does this for me it would probably be faster.

Is there a function that does this, or is there a way the Blt function can be set up to do this?