On NT/XP/2003 etc the first param to CallNextHookEx is ignored. See the documentation for CallNextHookEx:
http://msdn.microsoft.com/en-us/library/ms644974%28VS.85%29.aspx
c - How can I access a variable in a calling application from a dll? - Stack Overflow
操作系统不是太老的话，基本第一个参数忽略给0就好。不用使用共享内存去传递。
stack overflow 也提供了一些其他思路，比如通过导出函数去调用获取hhook。