units go in
<data>/unit/<unitname>
or
<data>/unit/<factionname>/<unitname>
textures go either in the "current dir" or in
<data>/textures/
for shared textures
likewise sounds either go in the current dir or
<data>/sounds
animations go in
<currentdir>/animations
sprites go in
<currentdir>/sprites
my paths work with flat data directories too :-)