On the top view of the grid in Hammer, whcih direction is front, left, back, and right for the skybox?

I guess left is left, front is north.

Just in case ure trying to texture the skybox directly, that's done with the tools/skybox texture helper, not with the seperate sky textures. Skyname is defined in the Map Properties.
Sky List with Pics here (http://www.hl2world.com/wiki/index.php/Sky_List),
Sky List with lighting recommendations here (http://forum.interlopers.net/viewtopic.php?t=3964).

Thanks.

Okay, so left on the top view grid is front.

I'm not really sure, North should be forward, but it might be like the funck_tracktrain orientation and be west :p