ArcGIS Engine 9.3 is a component of GIS, can be used to develop a geographic information system, you need to install VS2005 or 2008.
ArcGIS Server 9.3 is almost the same as the Engine, which is used for the development of large-scale GIS projects.
ArcGIS SDE 9.3 spatial database engine to establish a database.
ArcGIS IMS 9.3 used to build WEBGIS services!
Which ArcGIS Desktop 9.3
ArcGIS Engine 9.3
ArcGIS Server 9.3
are under the AO object!
The owner also left out an ESRI product: ArcGIS Mobile !