Hi,
Sybase Central is EOL.
I would download this soon if you would like to use this tool.
The tool taking over for Sybase Central is called Sybase Control Center (SCC).
If you want an interactive/gui isql session the tool is called DBISQL or also known as Interactive SQL.
This comes in the Sybase Central download (PC Client).
This can be also be accessed through Sybase Central tool itself.
In future releases DBISQL will be included in the SDK download.
Regards,
Ryan