We do have a product call Real UV, included with Shader Ops, that basically adds projection mapping based on real world sizes. For example you can tell it that this texture is 48" by 48", that it starts at X=20" and Y=16", and that it projects in the XY plane. You can download the demo at

Carrara 3.0
PC
http://digitalcarversguild.com/downloads/c3/shaderops.zip
Mac OS9
http://digitalcarversguild.com/downloads/c3/shaderopsos9.sit
Mac OSX
http://digitalcarversguild.com/downloads/c3/shaderopsosx.sit

Carrara 2.1
PC
http://digitalcarversguild.com/downloads/c2/shaderops.zip
Mac OS9
http://digitalcarversguild.com/downloads/c2/shaderopsos9.sit
Mac OSX
http://digitalcarversguild.com/downloads/c2/shaderopsosx.sit

Carrara 1.1
PC
http://digitalcarversguild.com/downloads/shaderops.zip
Mac
http://digitalcarversguild.com/downloads/shaderops.sit

It will be locked to the default values, but it will give you an idea of whether or not it will solve your problem.

Regards,
Eric Winemiller
Digital Carvers Guild
3D plug-ins for Carrara
http://digitalcarversguild.com

Eric Winemiller
Digital Carvers Guild
Carrara and LightWave plug-ins