haymaker said:
There's afew things that need to be correct for Hammer to recognize them

-you put them in materials/skybox?
-some skyboxes are not "finished" ie they're not set up to work with Source's formulas. You can check all dimensions and vmt's and stuff by referencing the relevant parts in this tut
http://forums.firearms-source.com/showthread.php?t=4539

Mine are placed in env/gfx .

They will only show if they are in the correct format, which is 256x256, 8bit tga's for memory and you have to put them in the right folder. Other than that, should be fine.

m82sniper said:
I've downloaded a bunch of new skyboxes to use, but I can't figure out how to get them working with Hammer. I have Hammer configured so it uses the Steam version of Half-Life. I'm not sure the default skyboxes are working either, don't remember adding them.

When creating your map, go to map properties, and find "skybox name" or anything like that. There, put the name of the skybox except for up, lf etc.

for example, if you have a skybox named cliff (like in half-life) there are files named clifflf, cliffdn etc. Remove the last 2 letters in that textbox and it should be fine.

There's afew things that need to be correct for Hammer to recognize them

-you put them in materials/skybox?
-some skyboxes are not "finished" ie they're not set up to work with Source's formulas. You can check all dimensions and vmt's and stuff by referencing the relevant parts in this tut
http://forums.firearms-source.com/showthread.php?t=4539