I keep getting lost in the mkmf code, so I was hoping to find a guide.

I have an extension that under Windows will use an external dll, but
under Unix the files are linked directly into the extension. So my
question is:

Can I explicitly exclude certain files in extconf.rb, that it has
found (by extension in the current directory) or (even better) can I
explicitly include source files in a different directory.

Thanks
pth