diff --git a/NEWS b/NEWS
index 1ba65ea..775ac31 100644
--- a/NEWS
+++ b/NEWS
@@ -1,3 +1,7 @@
+= Version 0.3.0 =
+
+Rudimentary support for writing zip archives.
+
 = Version 0.2.2 =
 
 Fixed and extended unit test suite. Updated to work with ruby/zlib
diff --git a/README.txt b/README.txt
index 2dd80ee..51d6eac 100644
--- a/README.txt
+++ b/README.txt
@@ -18,6 +18,9 @@ ruby-zlib: http://www.blue.sky.or.jp/atelier/#ruby-zlib
 
 This library requires ruby/zlib version 0.5.0 or newer.
 
+As of this writing ruby/zlib 0.5.0 is only available as
+ruby-zlib-0.5.0-pre3 at http://www.blue.sky.or.jp/atelier/ruby/
+
 
 = LICENSE =
 
diff --git a/zip.rb b/zip.rb
index c019fcd..d6ecfdb 100755
--- a/zip.rb
+++ b/zip.rb
@@ -453,7 +453,7 @@ module Zip
       @fileName = fileName
       @outputStream = File.new(@fileName, "wb")
       @entries = []
-      @compressor = NullCompressor
+      @compressor = NullCompressor.instance
     end
 
     def ZipOutputStream.open(fileName)
@@ -483,10 +483,12 @@ module Zip
     def finalizeCurrentEntry
       return unless @currentEntry
       finish
-      @currentEntry.compressedSize = @outputStream.tell - @currentEntry.localHeaderOffset - @currentEntry.localHeaderSize
+      @currentEntry.compressedSize = @outputStream.tell - @currentEntry.localHeaderOffset - 
+	@currentEntry.localHeaderSize
       @currentEntry.size = @compressor.size
+      @currentEntry.crc = @compressor.crc
       @currentEntry = nil
-      @compressor = NullCompressor
+      @compressor = NullCompressor.instance
     end
     
     def initNextEntry(entry, level = Zlib::DEFAULT_COMPRESSION)
@@ -520,13 +522,15 @@ module Zip
     end
 
     protected
-    def << (data)
-      @compressor << data
-    end
 
     def finish
       @compressor.finish
     end
+
+    public
+    def << (data)
+      @compressor << data
+    end
   end
 
 
@@ -538,22 +542,25 @@ module Zip
   class PassThruCompressor < Compressor
     def initialize(outputStream)
       @outputStream = outputStream
+      @crc = Zlib::crc32
       @size = 0
     end
 
     def << (data)
       val = data.to_s
+      @crc = Zlib::crc32(val, @crc)
       @size += val.size
       @outputStream << val
     end
 
-    attr_reader :size
+    attr_reader :size, :crc
   end
 
   class NullCompressor < Compressor
     include Singleton
 
     def << (data)
+      raise IOError, "closed stream"
     end
 
     attr_reader :size, :compressedSize
@@ -564,10 +571,12 @@ module Zip
       @outputStream = outputStream
       @zlibDeflater = Zlib::Deflate.new(level, -Zlib::Deflate::MAX_WBITS)
       @size = 0
+      @crc = Zlib::crc32
     end
     
     def << (data)
       val = data.to_s
+      @crc = Zlib::crc32(val, @crc)
       @size += val.size
       @outputStream << @zlibDeflater.deflate(data)
     end
@@ -578,7 +587,7 @@ module Zip
       end
     end
 
-    attr_reader :size
+    attr_reader :size, :crc
   end
   
   class ZipCentralDirectory
diff --git a/ziptest.rb b/ziptest.rb
index f7262aa..53f7b6c 100755
--- a/ziptest.rb
+++ b/ziptest.rb
@@ -551,7 +551,23 @@ class AbstractOutputStreamTest < RUNIT::TestCase
   end
 end
 
+
+module CrcTest
+  def runCrcTest(compressorClass)
+    str = "Here's a nice little text to compute the crc for! Ho hum, it is nice nice nice nice indeed."
+    fakeOut = AbstractOutputStreamTest::TestOutputStream.new
+    
+    deflater = compressorClass.new(fakeOut)
+    deflater << str
+    assert_equals(0x919920fc, deflater.crc)
+  end
+end
+
+
+
 class PassThruCompressorTest < RUNIT::TestCase
+  include CrcTest
+
   def test_size
     File.open("dummy.txt", "wb") {
       |file|
@@ -573,9 +589,15 @@ class PassThruCompressorTest < RUNIT::TestCase
       assert_equals(compressor.size, t1.size + t2.size + t3.size)
     }
   end
+
+  def test_crc
+    runCrcTest(PassThruCompressor)
+  end
 end
 
 class DeflaterTest < RUNIT::TestCase
+  include CrcTest
+
   def test_outputOperator
     txt = loadFile("ziptest.rb")
     deflate(txt, "deflatertest.bin")
@@ -608,8 +630,11 @@ class DeflaterTest < RUNIT::TestCase
       txt = inflater.read
     }
   end
-end
 
+  def test_crc
+    runCrcTest(Deflater)
+  end
+end
 
 class ZipOutputStreamTest < RUNIT::TestCase
   include AssertEntry
@@ -634,18 +659,33 @@ class ZipOutputStreamTest < RUNIT::TestCase
     assertTestZipContents(TEST_ZIP)
   end
 
-  def test_putOnClosedStream
-    fail "implement and expect ZipError"
-  end
-
   def test_writingToClosedStream
-    fail "implement this test and make sure behaviour is similar to closed File object"
+    assertIOErrorInClosedStream { |zos| zos << "hello world" }
+    assertIOErrorInClosedStream { |zos| zos.puts "hello world" }
+    assertIOErrorInClosedStream { |zos| zos.write "hello world" }
   end
 
   def test_cannotOpenFile
-    fail "implement and expect zip.closed? and exception from constructor"
+    name = "emptytestdir"
+    ensureDir(name)
+    assert_exception(Errno::EISDIR, "Is a directorYY") {
+      zos = ZipOutputStream.open(name)
+    }
   end
 
+  def ensureDir(name) 
+    return if File.stat(name).directory?
+    File.delete(name)
+    Dir.mkdir(name)
+  end
+
+  def assertIOErrorInClosedStream
+    assert_exception(IOError) {
+      zos = ZipOutputStream.new("test_putOnClosedStream.zip")
+      zos.close
+      yield zos
+    }
+  end
 
   def writeTestZip(zos)
     TEST_ZIP.entryNames.each {