public struct INTERNET_PROXY_INFO
        {
            public int dwAccessType;
            public IntPtr proxy;
            public IntPtr proxyBypass;
        }


        [DllImport("wininet.dll", SetLastError = true)]
        private static extern bool InternetSetOption(IntPtr hInternet, int dwOption, IntPtr lpBuffer, int lpdwBufferLength);


        private void RefreshIESettings(string strProxy)
        {
            const int INTERNET_OPTION_PROXY = 38;
            const int INTERNET_OPEN_TYPE_PROXY = 3;
            INTERNET_PROXY_INFO struct_IPI;
            struct_IPI.dwAccessType =
                INTERNET_OPEN_TYPE_PROXY;
            struct_IPI.proxy =
                Marshal.StringToHGlobalAnsi(strProxy);
            struct_IPI.proxyBypass =
                Marshal.StringToHGlobalAnsi("local");
            // Allocating memory
            IntPtr intptrStruct =
                Marshal.AllocCoTaskMem(Marshal.SizeOf(struct_IPI));
            // Converting structure to IntPtr
            Marshal.StructureToPtr(struct_IPI, intptrStruct, true);
            bool iReturn = InternetSetOption(IntPtr.Zero,
                                             INTERNET_OPTION_PROXY,
                                             intptrStruct,
                                             Marshal.SizeOf(struct_IPI));
        }




/CALL
RefreshIESettings("88.25.36.36:8080");
                    webBrowser1.Navigate("http://www.google.com");