For ArcGIS 8.x
ArcGIS does not currently support MakeStack functionality. Consequently, the function is not listed in the Command References. It is, however, available from the Raster Calculator interface and usage via the underlying Grid functionality.
For ArcGIS 9.x
The Composite Bands geoprocessing tool can be used to create Gridstacks or multiband raster datasets. The Composite Bands tool can be found in the Data Management Raster Toolset.