I just installed ArcGIS 9.3 and Hec-Georas 4.3.93 and the classic option is available. The classic option appears to allow the feature layers to be imported into a personal geodatabase, not a file geodatabase. Since I too was having the same errors with ArcGIS 10.0, my only option was to reinstall older versions of ArcGIS and HEC-GeoRas. This has been very frustrating, but the imports work fine using the older versions of both softwares - using the classic import into a personal geodatabase.