If I could get my hands on a recent version of AutoCAD....then you might see a model with an unprecedented level of detail. I'm pretty excited to be able to actually use my schooling for something finally....never thought it'd be with toy blocks however. =P
I have experience with both sets of tools (those for game developement and for CAD) and sadly the crossover of skills and technology is limited.
You will have to learn to use a whole new program and a whole new technique (albeit a more difficult one) for game development.
Milkshape 3D, Blender and 3DS Max all have plugins to enable DTS exporting for TGE and BL.
Milkshape is by far the simplest to use, but lacks many of the useful features and accuracy of Blender and 3DS Max. It is also only $35 I believe
Blender is free yet powerful modeling suite which I believe is capable of pretty much anything you'd need for BL. Rather complex and exporting can be temperamental.
3DS Max is by far the most powerful of the 3 but also the most expensive. Highly complex, but well documented.