Spec-wise, I'd recommend a system running, at the minimum:
- a 2GHz dual core processor
- 2GB of RAM
- a dedicated graphics card OR integrated ATI or NVIDIA graphics (not Intel. you want a more powerful chipset if you go this route)
- Windows operating system (for easier use with CAD software. Macs have somewhat fewer options and are more expensive, and Linux would be somewhat difficult to get SW running)
I'd also recommend springing for 64-bit Windows, since, at least on more powerful computers, it can take advantage of more resources and run a bit faster, especially since SW has a 64-bit version. The few remaining specs aren't quite as important to the functioning of SW or the system in general, so select everything else based on what you think you need
As for a specific recommendation, it would help to get a price range that you're looking at. There's a lot of good computers out there for CAD work, but if you're limited on what you can spend you're going to have to tweak some of the system specs to maximize your performance, and you may have to settle for lower specs than you might like. I can say that I can run Inventor pretty well on my system, and I'm running a somewhat older Inspiron 530 with a 2.53GHz Core 2 Duo with 2GB of RAM and a GeForce 9500GT graphics card, all of which I picked up open box for a pretty good deal. I'm pretty sure the total cost of my system comes out under $400, but I'll also say that as it stands now, it could probably use another Gig or two of RAM