Oracle Database Express Edition (XE)

Hi every body;
I have installed Oracle 10g XE for n-time, and for each new install I find new problems:
previously the welcome page http://127.0.0.1:8080/apex seems to work but I found a lot of problems so I decided to-reinstall the whole application.
but this time, even with every thing seems to work, I have not the access to the welcome page, here is the result of the configuration:

/ect/init.d/oracle configure

Oracle Database 10g Express Edition Configuration
-------------------------------------------------
This will configure on-boot properties of Oracle Database 10g Express
Edition. The following questions will determine whether the database should
be starting upon system boot, the ports it will use, and the passwords that
will be used for database accounts. Press <Enter> to accept the defaults.
Ctrl-C will abort.

Specify the HTTP port that will be used for Oracle Application Express [8080]:8081

Specify a port that will be used for the database listener [1521]:

Specify a password to be used for database accounts. Note that the same
password will be used for SYS and SYSTEM. Oracle recommends the use of
different passwords for each database account. This can be done after
initial configuration:
Confirm the password:

Do you want Oracle Database 10g Express Edition to be started on boot (y/n) [y]:y

Starting Oracle Net Listener...Done
Configuring Database...Done
Starting Oracle Database 10g Express Edition Instance...Done
Installation Completed Successfully.
To access the Database Home Page go to "http://127.0.0.1:8081/apex"

But :
ps -ef|grep oracle

oracle 21732 1 0 22:07 ? 00:00:00 /usr/lib/oracle/xe/app/oracle/product/10.2.0/server/bin/tnslsnr LISTENER -inherit
abouzaid 22037 20721 0 22:19 pts/0 00:00:00 grep oracle

and when i use (sqlplus system@XE):
the result:

SQL*Plus: Release 10.2.0.1.0 - Production on Thu Nov 9 22:09:38 2006

Copyright (c) 1982, 2005, Oracle. All rights reserved.

Enter password:
ERROR:
ORA-12514: TNS:listener does not currently know of service requested in connect
descriptor

please if any one can help!!!
I'm sorry for my english!!!!