The MeshCAM/Carbide Motion requirements are at
I think that the 4GB RAM is mainly for MeshCAM, which can consume a ton of memory. I'm running Carbide Motion on a used Dell Latitude E4200 running Win7 Pro that I bought just for the Nomad. It only has 2GB memory and runs CM fine. It's a 1.6GHz Intel Core2 Duo. The largest nc file I've loaded into CM is about 694k lines. Not run it yet for other reasons.
How does one go about updating the firmware to allow one to use other controller software?
I seriously doubt that would be possible. AFAIK the motion control is built into the Nomad controller board, and Carbide Motion is just sending high-level commands. But I could be all wrong.
Believe me, this weekend I was wishing for a step-and-direction input so I could control the Nomad through Mach3. I used CNCPro and TurboCNC in DOS for 8 years on my Sherline mill and lathe, and then my Tormach mill with Mach3 under WinXP for the last 8+ years, and this little Nomad scares me more than either. And I accidentally rapided a spinning face mill into the Tormach vise over the weekend. 1.5HP spindle and carbide inserts make big sparks...
But I'm at the bottom of the learning curve on the Nomad looking uphill right now. I'm thinking "this is scary fast" but in a couple weeks I know I'll be thinking "this is crazy fast!"