Half-transparent texture in 2 sided poly

Let's say I have a model which needs to have two sided texture which has some part visible and some part invisible. Hard to explain, but look at this image:



So for example if I have character which needs to have certain kind of hair: I make few polys to stick out from his head (dunno how to make "two sided polys", but i guess it's not difficult), and then I would have to assign to those polys a texture which have parts visible and invisible.

So (1) How do make this kind of texture, and (2) how do I make it so that it shows both sides of the poly?

The result should be similar to this creatures back hair:

The back hair itself is just a simple 2 sided plane that runs along the creature's back. The texture then is just hair with an alpha layer to break it up into the zig-zag formation you wish to aquire. Nothing as complex as you may think.

Just as I thought... But how do I add the alphalayer to Targa-file in Photoshop? I know that I'm supposed to select the 32bits/pixel option when saving the file, but how do I make it so that certain areas are invisible? I read the tutorial about basic modding and skinning, and it only taught how to make invisible sections in PSP.

So is it as easy in Photoshop as just selecting certain parts of the image and then deleting them (or erasing)? Or do I have to do something more complex?

First off you need the updated Targa pluggin for Photoshop 7, if you are using version 7 (The best version). That will allow you to save alpha channels.

There are two ways to make an alpha map.

1) Goto the image's 'Channel' section (Located as the second tab in the 'Layers' pallete) At the bottem of the pallete click 'Create New Channel' (Small paper icon). Everythin BLACK is alphaed (Transparent) everything WHITE is visible. You can only use black and white on this layer, however tones of grey can be used to increase or decrease opacity.

2) This is more for new users, and gnerally all you need if you are not going for real high detail. Just use the eraser tool. What you erase will show some white/grey checkered boxes. This is now alpha, or transparent. Whatever you want ot refer to it as.