Hi,
you can perform both depending on the best choice for your needs.

You could save diffuse and normals in a image near to this:

but without that ugly vertical white stripe in the middle xP

And build the UVmap using the left half of the image, so the normalmap coord into the shader will be:
Code:
float2 nCoor = inTex;
nCoor.x += 0.5f;


But as I suggested in my previous post, you could also use an effectmap, on same, twice or whatever resolution of the colormap:
Code:
float4 Color = tex2D ( sDiff, inTex );
float2 UpLeftQuarter = inTex * 0.5f;
float4 Normal = tex2D ( sEffects, UpLeftQuarter );
float2 UpRightQuarter = float2 ( UpLeftQuarter.x + 0.5f, UpLeftQuarter.y );
float4 Specular = tex2D ( sEffects, UpRightQuarter );
// and so...