Bear in mind that could bring maintenance complications. I assume by 'screen' you mean something between a net and the stuff chameleon cages are made of? You need to be wary that some fish need to breathe air (bettas and gouramis) and almost ALL fish need oxygen in the water, which comes from the water's surface moving whilst in contact with air.
I'm not saying you shouldn't, but these are things to take into account.
What I was thinking was more along the lines of creating a 'natural' impassable barrier - and aesthetic rock wall, or a divide blocked by plants.
If it is your first time, and you only have a 10 or 20 gallon enclosure, I would strongly discourage you from mixing animals. However, if you're anything like me you'll ignore my warning, in which case - be careful, and only go ahead if you're sure it won't be detrimental to the animals and/or you have the means to isolate and return an animal that doesn't 'work'.
A really great animal keeper is one who knows how to provide for the animal's needs whilst also making a good-looking display. I don't pretend to be one of those yet...
