Check this one:
http://forums.esri.com/Thread.asp?c=93&f=1147&t=133703
or this
http://help.arcgis.com/en/sdk/10.0/vba_desktop/conceptualhelp/index.html#//000100000027000000
Hi Yasmin
Frankly I do not want to practice VBA on top of ArcMap again. In case of doing the same thing in python (ArcPy) may be can give good advise.
However, in your code, i think you defined workspace (which is default for vector data) for raster you need to use RasterWorkspaceFactory/NewRasterWorkspace etc.