zlib && zip files

[Jan Prochazka]

Hi,
I need to decompress zip archive. I wrote a parser of zip file, i obtain 
the compressed data, but when i call zlib.decompress(data) on them,
it throws this error:

decbuf = decompressor.decompress(compressed_data)

error: Error -3 while decompressing: unknown compression method

I try to compress by zlib the same data which are in that file, the 
result was 6 bytes bigger, '\x78\xda' on begin and '\xc9\x1f\x87\x0b' on end
when i tried to put this extending data to zlib decompressor, it 
decompress some files of zip archive, but it fails, when i try to 
decompress 100MB file from archive

could you help, please?
thanks
Honza