The NED elevation dataset was projected from the geographic, NAD83 to UTM, Zone 18, NAD83. This was accomplished from ArcInfo command line of ArcGIS 9.1. The command line used to do this was:
NED_UTM18 = project(ned_37057094, geog2utm, bilinear).
Effectively what this does is project ned_37057094 using the parameters supplied in the file geog2utm using a bilinear interpolation method.
The contents of geog2utm are as follows:
INPUT
PROJECTION GEOGRAPHIC
UNITS DD
DATUM NAD83
PARAMETERS
OUTPUT
PROJECTION UTM
UNITS METERS
ZONE 18
DATUM NAD83
PARAMETERS
END