Sounds interesting, but I couldn't find out yet how you got it done with Global Mapper. I have a similar problem here. Downloaded some E00 files from the British Antarctic Survey into Global Mapper. They show fine there and I also can export them to DXF and see that they contain all altitude information.
Problem here is: SiteTopo can only load very limited amounts of data and crashes with most contour line files from Antarctica. Therefore I would be very interested to know how you converted your lines to a TIN (in the long run I need to get an elevation GeoTiff).
- Import the data in Global Mapper. Obviously it has to be 3D data.
- Open the "Overlay Control Center", that's the 4th button from the left, or Tools -> Control Center
- Right click on the layer name and pick the option "Create Elevation Grid from 3D Data". Go through the options there and make sure it does what you want to do (specifically, you'll want to tick the box that says "Save Triangulation Network (TIN) as a Vector Layer".
- Hit OK and off it goes.
This will, incidentally, also create an elevation raster, which you could export to GeoTIFF.