AutoCAD to ArchiCAD... DON'T DO IT!!! my opinion...
i have used acad for ~13 years and now have to work with archicad at the office since 2 years now... it's a pain in the a**! it's lacking so much basic functions of CAD and every single option is 2 or 3 times slower/more complicated compared to archicad...
eg.: to switch from box to cross selection you have to use a flyout!!! not like in acad or sketchup only drag left or right...
and it's the same to the most parameters you want to change - there's always an extra step to go...
And the biggest no-no for me is the missing block element! It's incredible, i think an easy to use block/component function is the core element of fast cad editing! It has to work just like in sketchup with it's components.
In archicad you can create an object, but how can you edit it?!? easy! explode it, make your changes, resave it and exchange the other objects of the same type with the new one!!! this was what i've been told by the graphisoft support! not worth discussing... and how about the base point of the new objects?!? are they still the same?!?...
And a last one: try to change the properties (like color, line type...) for a bunch of "different" object like lines, arcs, polylines, splines at once... in acad you can select as much different types as you like, all matching properties will be changed at once by one clic. In archicad you have to do this for every! object type seperately!!! (yes, lines, arcs, polylines and splines are counted as 4 separate types!!! )
and zooming/paning through a slightly bigger plan is soooo sloooow a can't believe it! i can copy the same plan 10x in acad and still work fluently.
I think when you're working with virtual building models with only simple objects and not much design changes after the first run, it's a nice app... But not for construction drawings or when you have many changes in your project.
And look at the prices of acad/acad lt and archicad! maybe an architectural tool set for acad would be the better choice...
Or take a look at Vectorworks. It has evolved very much in the last three years and is quite nice (i have worked with vw12/2008 for 1 year)
Just my opinion.
You should take a look at the demo version of archicad - then you will see...