I was wondering what the real limitations would be if I already have a 3d modeling program (Rhino 4.0) and use it in combination with LT? I have small residential architectural so might not need the full commercial version.Also, what is the real difference between Autocad 2010 Architecture and Autocad 2010 Commercial?Thanks

There are also other differences (than 3D) between LT and full AutoCAD - see e.g.:
http://www.cadforum.cz/cadforum_en/qaID.asp?tip=4452
 
It depends whether LT fits your needs.
 
The Architecture version adds special AEC objects like walls, doors, windows, stairs, roofs, columns, creating schedules, sections and controlling visibility for different views.

Thanks Vladimir. You are very helpful as usual.