Your net8 configuration was not successful.Just try to configure your net8 thru net8 configuration assistant utility which comes with oracle itself.
Try to find out whether ur listener has started or not by doing the follwing:
1]At command prompt type sqlplus
2]SQL> This will be shown to you.
3]Connect to internal/oracle
4]type lsnrctl and press enter
5]LSNRCTL> This will be shown to you
6]Then type status.This will give you the status of the listener.

Try to do the above and let me know as what is the problem you are getting now.

Gilbey