For Horizon ILS you need to install php-mssql it works for both Sybase and Microsoft DB.
In the …vufind/web/config/config.ini
driver = Horizon
Then check the Horizon.ini file
host = 192.168.1.101 ; better if you put de ip number
5000 ; 2025 or the port number that
you are using for the Sybase Server
username = sa
password = x76y8d9 ; the real password that you use in the SPUD for sybase
If these are OK, and you are receiving a 500 error… maybe you have a trouble with the apache/httpd settings.