Every time I use the displacement tool and create a brush, even on something simple, like a cube, it either 1) doesn't load, if I'm lucky or 2) when I test it, my server won't load the map.
I've tried all sorts of things, even just creating the displacement and moving nothing on it. Same thing happens.

What is it I'm missing?

Thanks

What does "doesn't load" mean? does it not compile? Check the log to see errors, or post here if you want.

Yeah if you could post your compile log that might turn something up. Also Im not sure how new you are to mapping but read up a bit to make sure you are doing everything correctly.

http://developer.valvesoftware.com/wiki/Displacements

That might be useful.

Basically, create a simple square brush (you dont need to create a more complex brush as you can mold the displacement once it is created). Then, if you are simply trying to create a ground, press ctrl+a to get the texture application window and select the top surface of the brush, and select create. Select any power, 3 is probably best perfomance wise, and click paint geometry and edit it. If this is what you have already done then I have no idea why it is not working Im afraid.

make sure you aren't trying to turn a brush that has anything less or more than 4 sides into a displacement, if it doesn't have 4 sides it wont be turned into one and the brush will get deleted.

i dont think thats the problem because he said even a cube wont work. make sure you dont have and func entities tied to it because dispalacements can't support funcs