Your ISP will have to have freetds libraries installed. PHP will have to have had the compile time option os --with-sybase=/path/to/freetds. Your best bet is to create a page that calls phpinfo(). In that page you can look at what configure options were specified. If it already has the --with-sybase option, then you can probably can move on to the next step. Otherwise you are going to have to request that your ISP recompiles PHP.
They will then need to add an entry into the interfaces file for your SQL server(Basically creating a DSN pointing to your SQL server). You will then reference the connection name, instead of an address, in your connection string.
