i solved the problem compiling mysqlclient module under win98 using vc++ 6.
-setted run-time library to: debug multi-threaded
-object modules added:wsock32.lib mysqlclient.lib
-include files targeted when compiling: /I "c:\mysql\include"
-windows.h,mysql.h included
-linking-excluded libcmt module: /nodefaultlib:"libcmt"

and voila, it should work...