Hi, Clara -
        I know you can create your own patterns and texture libraries in
illustrator. I would think that would be a lot easier than layering a
texture block under a window in your art (if I read your question
correctly). When you create a new pattern, you can then fill any area
using the regular fill command.
        I work in Illus 7 now; you can use any pattern in any Illus. 7 document
as a pattern. I don't know about other versions, as they don't use the
swatches, but I seem to remember that you can import patterns there too.

Good luck!
Gail