ftp://ftp.blm.gov/pub/gis/sdts/dem/sdtsepov.zip is a program that will convert SDTS files to TGA files which can be imported to Vue. http://software.geocomm.com/translators/script_dem2tga.html is a program that will convert USGS DEM files to TGA files. A VistaPro DEM file is completely different from a USGS DEM file. VistaPro itself can export its heightfields as a TGA. The best utility to use for heightfield conversion and generation is Leveller: http://www.daylongraphics.com/products/leveller/index.htm