I used to own a MSI Wind U100 with 2GB of RAM and a 500GB hard drive and I honestly never really had a problem. The keyboard and mouse pads are small on them but a week into use and I was used to it, never really had a problem.
For your uses I would say a good netbook would be fine. I was able to play a good portion of 3D games (Unreal Tournament 2004, anything Quake 3 engine based, etc.) so I wouldn't see 2D CAD being much of a strain.
I say get one locally, try it out, and if it doesn't work return it and get something better. There is a whole slew of 15.4in laptops now a days with more than decent performance in the sub-$400 range.
Its all personal preference in my opinion, performance was never really an issue with my Wind, it was just getting past the size of the keyboard and touch pad. Most have a resolution of 1024x678 or something like that, so surfing the web was never an issue.