After Installing Zabbix Server at Ubuntu/Centos how to add window zabbix Client ?

Create a configuration file.

Create a configuration file c:/zabbix_agentd.conf (it has a similar syntax to the UNIX agent configuration file).

An example configuration file is available in Zabbix source archive as conf/zabbix_agentd.win.conf.

Install agent as a Windows service.

zabbix_agentd.exe --install

If you wish to use a configuration file other than c:\\zabbix_agentd.conf, you should use the following command for service installation

zabbix_agentd.exe --config <your_configuration_file> --install

A full path to the configuration file should be specified.

Run agent.

Now you can use Control Panel to start the agent service or run:

zabbix_agentd.exe --start

Configuration

To perform active checks on a host Zabbix agent needs to have the hostname defined. Moreover, the hostname value set on the agent side should exactly match the ”Host name” configured for the host in the frontend.

The hostname value on the agent side can be defined by either the Hostname or HostnameItem parameter in the agent configuration file - or the default values are used if any of these parameters are not specified.

The default value for HostnameItem parameter is the value returned by the “system.hostname” agent key and for Windows platform it returns the NetBIOS host name.

The default value for Hostname is the value returned by the HostnameItem parameter. So, in effect, if both these parameters are unspecified the actual hostname will be the host NetBIOS name

also you can use forum

https://www.zabbix.com/forum/showthread.php?t=803

https://www.zabbix.com/documentation/1.8/manual/processes/zabbix_agentd_win