If You are missing the zlib1.dll from your computer then download it from here:
ZLIB1.DLL
Then Install Like So:
If you are using 32/64-bit version of Windows: (C:\Windows\System32 (Windows XP, Vista, 7))
If you use a 64-bit version of Windows, you should also place zlib1.dll in (C:\Windows\SysWOW64\)