how to save tranparency in Jacs photoshop

I want to make a wingless doom guard so I want to make the doom guard's wings transparent, but when I save it in Jasc, I can only choose a 8-bit, 16-bit or 24-bit targa file and none of these support transparency. SO HOW DO I DO IT? (I have the demo version) and how do you make team colours?

1. You cannot create team colours in skinning. You can do that in modelling. If you want team colours, set it in the object editor for the unit. Some models may not have team colours though.

but how do you save transparency? When I try it syas that, because when I try to save as Targa it says that it can only save one alpha channel, while it doesn't change any previous transparency it turn my transparency to white. So how do I save it?