Parsing the format isn't the problem. The problem is actually doing something with what you're parsing. Zip files can contain encryption and various extensions, all of which would be far beyond what mIRC scripting could process in a remotely useful timescale. Even ignoring those extras, the basic decompression methods that aren't included as built-in mIRC identifiers (ie. those which don't use the standard DEFLATE algorithm) will be too slow to be useable.
