tinted transparency

I,m doing a re-paint of a Blackhawk using the paint kit from hovercontrol.com. It's all done no problem using photoshop to paint the textures and BMP them then Dxtbmp to convert them to extended as well as apply an alpha channel to the black areas. The only thing is the window areas are completely clear, which looks a bit odd as if there's no glass. Previewing the transparency in Dxtbmp shows the alpha areas completely clear, straight through to the white/grey checkerboard. when I compare it to the standard Blackhawk ( using FS repaint as a viewer ) it has tinted transparent windows, 5% black or something similar.http://www.hobra.net/hc-images/tinted.jpgNotice how on the defult textures the windows are tinted and on my repaint they are compleatly clear, as if there is no glass in there. It just looks a bit weird.The help page in Dxtbmp speaks about the formats that it supports that have varying levels of transparency (eg. DXT3 formats have a 4 bit Transparency giving 16 levels of transparency ) but not how to acheive those levels. I'm at a loss. I also have imagetool though I'm not sure what to do with that either.So to my question, how do I create tinted transparent areas for the windows?