Yes, it should still run on older machines. Perhaps a little slower though. My "field" laptop is a 1.2 Ghz with 256 mg RAM and 16 mb video and it runs much faster than the previous version. Just have a few graphical bugs to work out.
The Landsat imagery is ~15 meter at the highest resolution. You'll get slightly better detail in the new D3D TopoFusion, but it's not really noticeable.