Steve,
Welcome to the forums and to Cartographica. NAD83 and WGS84 are indeed slightly different. If you need pure WGS84-based UTM Zone 45N, you can go to SpatialReference.org and download the EPSG:32645 projection file and then drag it into Cartographica's Set Projection window and it will be available for you to use (labeled WGS 84 / UTM zone 45N).
If you still find that things aren't lining up, please contact us through support and we can work with you to locate the specific problems.