mmmh!
nothing to do!
I insert a block width image on C:\Program Files\AutoCAD Map 3D 2009\Sample\db_samp.dwg file
and I wrote two xml files (the difference is only the name of block in blockname tag)
the fisrt work width this point style with an graphic block:
false
false
Centimeters
DeviceUnits
0.3
0.3
0.0
C:\Program Files\AutoCAD Map 3D 2009\Sample\db_samp.dwg
CHAIR7
FFC69C6D
FF726358
the second does not work width this point style with an image block:
false
false
Centimeters
DeviceUnits
0.3
0.3
0.0
C:\Program Files\AutoCAD Map 3D 2009\Sample\db_samp.dwg
person
FFC69C6D
FF726358
in the enhanced stylization options and the document that you've suggested (building_symbol_libraries_with_autodesk_mapguide_enterprise_2009.pdf) I have not found solution.
But a specific reference could be reading this sentence:
The image itself may either be specified in the Content element as base 64 encoded PNG.
I will try tomorrow with a similar image
regards
andrea