Sky box problem

On several maps ive downloaded, for some reason i see the sky as , well, er, it’s hard to explain, so i’ll give you a pic:

It’s very annoying, if i look down then up, i get repeating images of what i just looked at on the sky. and commonly occurs on maps i download that have missiong textures (probably due to them using CS textures, that i lack) however, on GM_excess construct i see no missing textures and the level itself seems pretty awesome, but the sky thing makes it impossible to play.

my question is, how do i fix it?

Get the skybox material.

A lot of maps use counter-strike skyboxes.

How? where? and how do i find out whitch one it uses?

Only (legal) way is to buy Counter Strike.

99% percent chance it’ll be a CS:S skybox