where u able to start the listener?
are u using TNS_ADMIN?
Enable tracing for more information.

May be, there is too much of load in the same port.
so edit the listener.ora in 9i home to seperate 9i and 8i connections in seperate ports...ie listen in seperate ports.
so that you can have a 
lsnr_9i listening in 1521 and
lsnr_8i listening in 1526

1. lsnrctl start -- starts the lisnter.
   where u able to do this?
   then check the status
   lsnrctl status
2.
quoting oracle docs

[b]Setting Trace Parameters Using Component Configuration Files[/b]

To set tracing parameters using component configuration files: 

Specify the following parameters in the component configuration file (SQLNET.ORA, LISTENER.ORA, NAMES.ORA, or CMAN.ORA): 
TRACE_LEVEL_component name=(OFF/USER/ADMIN/SUPPORT)
TRACE_DIRECTORY_component name=directory name

If you modified the configuration files while the component was running, start or restart the component to enable the changed parameters. 

[b]Setting Trace Parameters Using Component Control Utilities[/b]

To set trace parameters using component control utilities: 

For the listener, use the TRACE command from the Listener Control Utility, to set the trace level while the listener is running; 
For Oracle Names, use the SET TRACE_LEVEL command from the Names Server Control Utility, to set the trace level while the Names Server is running. Note: 

For Oracle Connection Manager, the trace level can only be set from the configuration file, CMAN.ORA  
 
 
[b]Using the Trace Assistant to Examine Your Trace Files[/b]

Net8 provides a tool called the Trace Assistant to help you understand the information provided in your trace files by converting existing lines of trace file text into a more readable paragraph. Note that the Trace Assistant runs against only a level 16 (SUPPORT) SQL*Net or Net8 trace file. 

To run the Trace Assistant, type the following at any command line prompt: 

trcasst [[options]] filename

3. example for a listener.ora

### assume all these entries are in a single listner.ora in $ORACLE9I_HOME/network/admin
# 8i Listener Service

LSNR_8i =
  (DESCRIPTION_LIST =
    (DESCRIPTION =
      (ADDRESS_LIST =
        (ADDRESS = (PROTOCOL = IPC)(KEY = EXTPROC))
      )
      (ADDRESS_LIST =
        (ADDRESS = (PROTOCOL = TCP)(HOST = xxxxxx )(PORT = 1526))
      )
    )
  )

# 9i Listener Service

LSNR_9i =
  (DESCRIPTION_LIST =
    (DESCRIPTION =
      (ADDRESS_LIST =
        (ADDRESS = (PROTOCOL = TCP)(HOST = xxxxx )(PORT = 1521))
      )
    )
  )

# intances registered to lsnr_9i
SID_LIST_LSNR_9i =
  (SID_LIST =
    (SID_DESC =
      (ORACLE_HOME = /u01/app/oracle/product/9.2.0)
      (SID_NAME = 9idb1)
    )
    (SID_DESC =
      (ORACLE_HOME = /u01/app/oracle/product/9.2.0)
      (SID_NAME = 9idb2)
    )
    (SID_DESC =
      (ORACLE_HOME = /u01/app/oracle/product/9.2.0)
      (SID_NAME = 9idb3)
    )
  )

#instances registered to lsnr_8i

SID_LIST_LSNR_8i =
  (SID_LIST =
    (SID_DESC =
      (ORACLE_HOME = /u01/app/oracle/product/8.1.7)
      (SID_NAME = 8idb1)
    )
    (SID_DESC =
      (ORACLE_HOME = /u01/app/oracle/product/8.1.7)
      (SID_NAME = 8idb2)
    )
  )

# usage for lsnrctl
#		now 
#		lsnrctl start LSNR_9i -- will start listener LSNR_9i in 1521 and listens for 9i database requests		
#		lsnrctl start LSNR_8i -- will start listener LSNR_8i in 1526 and listens for 8i database requests		
# similarly
#		lsnrctl stop LSNR_9i
#		lsnrctl stop LSNR_8i
#		lsnrctl status 	LSNR_9i
#		lsnrctl status 	LSNR_8i