Oracle Database Discussions

I have installed Oracle 8.1.7 on a HP machine which already had Oracle 8.0.4.

Currently I am able to use the database on Oracle 8.1.7. But I am not able to use the database on Oracle 8.0.4.

FYI, I have not modified the listener.ora of both the version. I have also not modified the tnsnames.ora of both the version.

My questions are (Please understand that I am doing all this for the first time)
1. Do I need two tnsnames.ora files. Can I merge them. If yes, where do I move the file. What should I do after moving the file?
2. I plan to keep listerner.ora separately for both the version, since they are under different homes.

FYI, if I start the database on version 8.0.4 using svrmgr, I get the following error..
SVRMGR> startup
ORACLE instance started.
Total System Global Area 113822444 bytes
Fixed Size 47852 bytes
Variable Size 93220864 bytes
Database Buffers 20480000 bytes
Redo Buffers 73728 bytes
ORA-03113: end-of-file on communication channel

Similarly if I try to see the status on lsnrctl I get the following error messages..
Connecting to (ADDRESS=(COMMUNITY=lsco_tcp.some.com)(PROTOCOL=TCP)(Host=tyoux
)(Port=1526))
TNS-12224: TNS:no listener
TNS-12541: TNS:no listener
TNS-12560: TNS:protocol adapter error
TNS-00511: No listener
HPUX Error: 239: Connection refused

Thanks a lot for your helps.