Thanks for the reply. The other Transparency Attributes all seem to work fine but dont suffice for what I need (see below). I'll keep trying, maybe I need to read more about how it works in opengl and then backtrack through the code.
I have a series of Quad Array shapes and want sections of their texture to appear 100% transparent, like holes have been cut in it. In blended mode, whilst it works, I get an xray effect where I can see straight through other sections of the same shape, which I believe there is no work around for. However, I think screen door mode should allow this as the transparency is done in the opaque phase and I am happy to sacrifice some quality to achieve this.