The fastest way of doing it is making a big sphere and texturing it. In this example, you could use the file sky.bmp in the example "jetski".
sync on
make object sphere 1,5000
set object 1,1,1,0 :`this will make the sphere so that you can see it even if you are inside it.
REM Because making the sphere will move the camera, set the new location
position camera 0,0,0
load image "C:\Programas\Dark Basic Software\Dark Basic\myproj\JetSki\sky.bmp",1
REM Make sure you change this destination. It is where the file is in MY computer!
texture object 1,1
do
REM If you want the sky not to be static, rotate it
y#=wrapvalue(y#+.18)
yrotate object 1,y#
REM Control Camera Angles
ya#=wrapvalue(ya#+mousemovex() )
xa#=wrapvalue(xa#+mousemovey() )
rotate camera xa#,ya#,0
sync
loop
Hope this answer you!