I'm moving my Wireshark development environment from a win32 machine to a 64-bit one.
I use it for developing plugins, which I assume users will soon want in both 32 and 64-bit versions,
        cl -DWIN32 -DNULL=0 -D_MT -D_DLL -WX -DHAVE_CONFIG_H /I. /I.. /ID:\wireshark-win32-libs-1.4\
gtk2\include\glib-2.0  /ID:\wireshark-win32-libs-1.4\gtk2\lib\glib-2.0\include  /ID:\wireshark-win32
-libs-1.4\WPdpack\include -D_U_="" /Zi /W3 /MD /D_CRT_SECURE_NO_DEPRECATE /D_CRT_NONSTDC_NO_DEPRECATE /DWIN32_LEAN_AND_MEAN /DMSC_VER_REQUIRED=1600 /D_BIND_TO_CURRENT_CRT_VERSION=1 /MP -Fd.\ -c file_util.c 
inet_aton.c inet_ntop.c inet_pton.c mpeg-audio.c privileges.c str_util.c type_util.c strptime.
c unicode-utils.c wsgetopt.c
Microsoft (R) C/C++ Optimizing Compiler Version 16.00.30319.01 for x64
Copyright (C) Microsoft Corporation.  All rights reserved.
        link  /INCREMENTAL:NO /NOLOGO -entry:_DllMainCRTStartup@12 -dll kernel32.lib  ws2_32.lib msw
sock.lib advapi32.lib  /DEBUG /MACHINE:x86   /DEF:libwsutil.def /OUT:libwsutil.dll  /IMPLIB:libwsutil.lib  ..\image\libwsutil.res  file_util.obj             inet_aton.obj           inet_ntop.obj        inet_pton.obj           mpeg-audio.obj  privileges.obj  str_util.obj    type_util.obj  strptime.obj
                 unicode-utils.obj       wsgetopt.obj D:\wireshark-win32-libs-1.4\gtk2\lib\glib-2.0.
lib  D:\wireshark-win32-libs-1.4\gtk2\lib\gmodule-2.0.lib  D:\wireshark-win32-libs-1.4\gtk2\lib\gobject-2.0.lib
file_util.obj : fatal error LNK1112: module machine type 'x64' conflicts with target machine type 'X86'
NMAKE : fatal error U1077: '"C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\Bin\amd64\link.EXE"' : return code '0x458'
NMAKE : fatal error U1077: '"C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\Bin\amd64\nmake.exe"' : return code '0x2'