Depends on how intensive the work you're going to be doing on autocad is.
As a general statement, so long as you're not doing anything massively intensive then a GTX 460 would suffice. I'm unsure if the Autodesk applications make use of CUDA (i swear i read somewhere they do though). But if they do that's an added bonus.
The GTX 460 is a consumer model (as cheap as $140), if you want the professional models look at the Quaddro's or the Firepro's from AMD. They are a lot more expensive ($2000 generally) but are generally more specialised for the type of work you're doing and have a guaranteed 24 hr replacement service incase it goes faulty.
I would expect the systems to run quadcores, quadro gpu's, and at least 4gb of DDR2 RAM? Are your current computers prebuilts or all custom built?
With Revit, smooth performance would desire quadro cards/firepro cards...or simply workstation cards. They cost alot more then the average desktop user cards or enthusiast ones.
If they have quadro's already, I would stick with them over consumer graphic cards.
Better yet, how many do you need?