Try in a command window: netstat -bv
This will list the application that is currently using the FTP port.
As for Open Office, I don't think it is the FTP port that is blocking the start of Open Office. I once had the same problem with Open Office not starting. Turned out is was unable to determine default language for the gui (even if it is not displaying the gui). Started it once manually with gui, copied the resulting config directory to the alfresco open office config directory. Sorry I cannot remember paths.
/Peter Löfgren