zabbix_agentd.exe gives this error when run on pre Windows XP systems:
zabbix_agentd.exe - Entry Point Not Found
The procedure entry point freeaddrinfo could not be located in the dynamic link library WS2_32.dll.

See http://www.zabbix.com/forum/showthread.php?p=39592 for discussion

Probable solution from http://msdn.microsoft.com/en-us/library/ms737931(VS.85).aspx
Support for freeaddrinfo on earlier versions of Windows

The freeaddrinfo function was added to the Ws2_32.dll on Windows XP and later. To execute an application using this function on earlier versions of Windows (Windows 2000, Windows NT, and Windows Me/98/95), then you must include the Ws2tcpip.h file and also include the Wspiapi.h file. When the Wspiapi.h include file is added, the freeaddrinfo function is defined to the WspiapiFreeAddrInfo inline function in the Wspiapi.h file. At runtime, the WspiapiFreeAddrInfo function is implemented in such a way that if the Ws2_32.dll or the Wship6.dll (the file containing freeaddrinfo in the IPv6 Technology Preview for Windows 2000) does not include freeaddrinfo, then a version of freeaddrinfo is implemented inline based on code in the Wspiapi.h header file. This inline code will be used on older Windows platforms that do not natively support the freeaddrinfo function.