Hey, I'm using a skybox for my sky and want to know how to make the images blend and not cut each other off. Any help?
If you render them in one of the various programs that can do nice sky, you usually just have to set the camera field of view correctly and take a picture from the same position facing in each direction. You should be able to find a tutorial on google for whatever software you choose. I use Bryce just because I had it already, it's ok.
can't the skybox be rendered as dome-like as it does in Blender3D or does it have to be really a box?
yes, these are called SkySpheres or if you just want half a sphere (the top half), its called SkyDome.
Skysphere is easy, just render the SkySphere texture to a Sphere.