Does u,v,w texture mapping exist?

For mapping a cubemap texture, do we need 3 texture coordinates like u,v and w. I can't seem to find such a thing in DX9 documentation? Without the third element, can we index a mesh into the center of it, or anywhere between? {0, 12, D3DDECLTYPE_FLOAT2, D3DDECLMETHOD_DEFAULT, D3DDECLUSAGE_TEXCOORD, 0}, to {0, 12, D3DDECLTYPE_FLOAT3, D3DDECLMETHOD_DEFAULT, D3DDECLUSAGE_TEXCOORD, 0}, Thanks Jack