I know that turning on the transparency switch in the Texture palette will make all 100% black areas transparent. In a similar way, pressing the Hide Points will make the darker parts of an object transparent. In both cases, the transparency is either ON or OFF, no half way, quarter way, three fifths way…
My question is, is there a way to vary the degree of transparency, using materials or something? 
Thanks for any help.
'Evening Muvlo . . .
You asked, “is there a way to vary the degree of transparency”, yes. If you go into the “Material/Modifiers” of most of the Materials & go down to the “Transparency” adjuster, you can set it from 0 to 100. You can also get varying results by using the “Transparency Curves” adjuster. If you set the Transparency to, let’s say 75, then play with the Transparency Curves adjuster, you’ll find that you can get very different results with a transparent object. The only thing to remember is: Make sure you have the “Render/Modifiers/Flatten Layers” switch off . . . ( being non-green ), & you’ll seem to get more transparency in BEST render mode 
I hope this helps some & have a good one . . . 
Mark.
PS: ( Make sure you have the objects with transparency on a separate layer above all the other layers, & you’ll need an image of something on the lower layer or layers to see through the transparent objects. )
Kruzr said most of it, but the main one I would emphasize is the transparency graph…varying this gives you an incredible range of effects. Also, if you pull a point outside the graph ‘frame’, then bring it back in, you can make square, ‘stairstep’ transitions…try that and I know you’ll get some interesting new ideas!! 
I agree with stonecutter.
The graph is the key to some seriously nice transparancy maps.
Hi Muvlo, from your question it sounds like you wish to use texture maps and have portions of these textures to be partially transparent? As you’ve noted this is not possible but perhaps a combo of texture map and material will achieve your goal.
For example if I had a texture map of the nose of a plane I wanted to apply to a sphereinder, I would color the cockpit windows pure black in the texture map then apply and activate the “transparent” button in the texture panel. Only problem is now it just looks like I have no windows on my plane, totally transparent. I would then add a second (ever so slightly shrunk) sphereinder with a basic material (no texture) with the transparency set appropriately to simulate the windows. Perhaps!! Muvlo, I’ve no idea if this would actually work or what you even want - just an idea, good luck!
jd
Thanks for your suggestions! Though I’m not working on an image that calls for this at the moment, I’ve been wondering about this kind of thing…
Time to go experiment
Thanks again.
Make sure you put it on a differnt (LAYER) when you experiment.