just in case anyone else is still coming across this problem...the backup program 'idrive' will install an old zlib1.dll into the windows system32 directory, which conflicts with gimp.
since i rely on idrive, i worked around the problem by copying gimp's zlib1.dll from gimp's bin directory into lib\gimp\2.0\plug-ins.
The Gimp team needs more Windows devs (they say so on their own site) so odds are you will run into more bugs on Win7 than GNU/Linux or BSD unfortunetly
gzdirect is missing in the zlib1 dll file. dll is a dynamic library link (It has to be linked to it to make it work correctly) You can try to search for it, and put it back in the folder or uninstall program, and download it again and reinstall. That should work.
Thank you for the helpful reply but I resolved the problem this week. after asking around in Gimper.net someone suggested to rename the zlib1.dll located in the win32 folder and copy the one from gimp into the win32 folder. i worried whether the action would affect the compatibility of my installed programs, so i kept the original zlib1.dll in the win34 folder. then i found Gimps miss placed zlib1.dll and returned it to its bin folder.
since i rely on idrive, i worked around the problem by copying gimp's zlib1.dll from gimp's bin directory into lib\gimp\2.0\plug-ins.
I should up date the discretion box soon.