I work in an architecture firm. We use 8600GT's the normal machines and they do run fine. But if you are going to do anything with textures or renderings, you will want something better. Especially if you plan on doing lots of work in 3D. Anything will 'work' but if you want good performance, you need something better.
The quadro cards do have great support and drivers, but they are very pricey. It is possible to flash certain cards to their Quadro counterparts, but I'm not sure if it is worth it.
It takes forever to render with onboard, yes, but Im saying if you get a 4670 it'll be perfect for what he needs.