First of all : your icons are tha bomb !
to help you with the tga:
i assume you use Photoshop so here we go
create your icon on a transparent background (you can choose this by selecting in the new file dialog box , background = transparent)
after creating your icon :
-click the select tool
-press ctrl+a
-edit >> copy Merged
-file new (transparent background)
-ctrl+v
-take a deep breath

-tap and hold the ctrl button and click in the layerspane on the square that is in front of your layer name
(this will select your icon as a whole)
-in the layers pane click the alpha tab, at the bottom of the layers pane there is an icon that allows you to create a new layer, click that one
-edit -fill- color:white
-now make sure that all layers in the alpha layers pane are visible (click the eye in front of the layer, so RGB, red, green, blue and the one you created should be visible
-file - save as - tga - make sure to click the 32 bit version, because only in the new wisbar software the 24bit version is supported
I hope i did not miss any step because i dont got a Photoshop on this computer, i can recheck my post when I come home, if my plane is not delayed that is
Hope this was usefull