Do you mean running the Android apps on original Maemo OS?
In that case: yes it is theoretically possible but would take some work
http://talk.maemo.org/showthread.php?t=32784

Do you mean running the complete Android OS on the N900?
In that case yes as well. But it would probably take many years to make it run with all functionality. One would have to find drivers and replace all binary blobs.