diff --git a/Mac/BuildScript/build-installer.py b/Mac/BuildScript/build-installer.py
index 75cbf0a..7ffb065 100755
--- a/Mac/BuildScript/build-installer.py
+++ b/Mac/BuildScript/build-installer.py
@@ -10,7 +10,7 @@
 Usage: see USAGE variable in the script.
 """
 import platform, os, sys, getopt, textwrap, shutil, urllib2, stat, time, pwd
-import grp
+import grp, md5
 
 INCLUDE_TIMESTAMP=1
 VERBOSE=1
@@ -31,6 +31,8 @@
     def writePlist(plist, path):
         plist.write(path)
 
+
+
 def shellQuote(value):
     """
     Return the string value in a form that can safely be inserted into
@@ -62,7 +64,7 @@
 # The directory we'll use to store third-party sources. Set this to something
 # else if you don't want to re-fetch required libraries every time.
 DEPSRC=os.path.join(WORKDIR, 'third-party')
-DEPSRC=os.path.expanduser('~/Universal/other-sources')
+DEPSRC=os.path.expanduser('/tmp/other-sources')
 
 # Location of the preferred SDK
 SDKPATH="/Developer/SDKs/MacOSX10.4u.sdk"
@@ -94,8 +96,9 @@
 # batteries included python.
 LIBRARY_RECIPES=[
     dict(
-        name="Bzip2 1.0.3",
-        url="http://www.bzip.org/1.0.3/bzip2-1.0.3.tar.gz",
+        name="Bzip2 1.0.4",
+        url="http://www.bzip.org/1.0.4/bzip2-1.0.4.tar.gz",
+        checksum='fc310b254f6ba5fbb5da018f04533688',
         configure=None,
         install='make install PREFIX=%s/usr/local/ CFLAGS="-arch %s -isysroot %s"'%(
             shellQuote(os.path.join(WORKDIR, 'libraries')),
@@ -106,6 +109,7 @@
     dict(
         name="ZLib 1.2.3",
         url="http://www.gzip.org/zlib/zlib-1.2.3.tar.gz",
+        checksum='debc62758716a169df9f62e6ab2bc634',
         configure=None,
         install='make install prefix=%s/usr/local/ CFLAGS="-arch %s -isysroot %s"'%(
             shellQuote(os.path.join(WORKDIR, 'libraries')),
@@ -118,6 +122,7 @@
         name="GNU Readline 5.1.4",
         url="http://ftp.gnu.org/pub/gnu/readline/readline-5.1.tar.gz" ,
         patchlevel='0',
+        checksum='7ee5a692db88b30ca48927a13fd60e46',
         patches=[
             # The readline maintainers don't do actual micro releases, but
             # just ship a set of patches.
@@ -129,9 +134,9 @@
     ),
 
     dict(
-        name="SQLite 3.3.5",
-        url="http://www.sqlite.org/sqlite-3.3.5.tar.gz",
-        checksum='93f742986e8bc2dfa34792e16df017a6feccf3a2',
+        name="SQLite 3.3.14",
+        url="http://www.sqlite.org/sqlite-3.3.14.tar.gz",
+        checksum='e1a4428a5cb17f28164731b72f06130a',
         configure_pre=[
             '--enable-threadsafe',
             '--enable-tempstore',
@@ -144,6 +149,7 @@
     dict(
         name="NCurses 5.5",
         url="http://ftp.gnu.org/pub/gnu/ncurses/ncurses-5.5.tar.gz",
+        checksum='e73c1ac10b4bfc46db43b2ddfd6244ef',
         configure_pre=[
             "--without-cxx",
             "--without-ada",
@@ -172,6 +178,7 @@
     dict(
         name="Sleepycat DB 4.4",
         url="http://downloads.sleepycat.com/db-4.4.20.tar.gz",
+        checksum='d84dff288a19186b136b0daf7067ade3',
         #name="Sleepycat DB 4.3.29",
         #url="http://downloads.sleepycat.com/db-4.3.29.tar.gz",
         buildDir="build_unix",
@@ -321,6 +328,17 @@
         fatal("Please install the latest version of Xcode and the %s SDK"%(
             os.path.basename(SDKPATH[:-4])))
 
+    if os.path.exists('/sw'):
+        fatal("Detected Fink, please remove before building Python")
+
+    if os.path.exists('/opt/local'):
+        fatal("Detected MacPorts, please remove before building Python")
+
+    if not os.path.exists('/Library/Frameworks/Tcl.framework') or \
+            not os.path.exists('/Library/Frameworks/Tk.framework'):
+
+        fatal("Please install a Universal Tcl/Tk framework in /Library from\n\thttp://tcltkaqua.sourceforge.net/")
+
 
 
 def parseOptions(args = None):
@@ -457,6 +475,17 @@
         except:
             pass
 
+
+def verifyChecksum(path, checksum):
+    summer = md5.md5()
+    fp = open(path, 'rb')
+    block = fp.read(10240)
+    while block:
+        summer.update(block)
+        block = fp.read(10240)
+
+    return summer.hexdigest() == checksum
+
 def buildRecipe(recipe, basedir, archList):
     """
     Build software using a recipe. This function does the
@@ -478,13 +507,15 @@
         os.mkdir(DEPSRC)
 
 
-    if os.path.exists(sourceArchive):
+    if os.path.exists(sourceArchive) and verifyChecksum(sourceArchive, recipe['checksum']):
         print "Using local copy of %s"%(name,)
 
     else:
         print "Downloading %s"%(name,)
         downloadURL(url, sourceArchive)
         print "Archive for %s stored as %s"%(name, sourceArchive)
+        if not verifyChecksum(sourceArchive, recipe['checksum']):
+            fatal("Download for %s failed: bad checksum"%(url,))
 
     print "Extracting archive for %s"%(name,)
     buildDir=os.path.join(WORKDIR, '_bld')
@@ -663,7 +694,6 @@
         for dn in dirnames:
             os.chmod(os.path.join(dirpath, dn), 0775)
             os.chown(os.path.join(dirpath, dn), -1, gid)
-            
 
         for fn in filenames:
             if os.path.islink(fn):
@@ -1010,6 +1040,7 @@
             shellQuote(tmpPath),
         ))
 
+
 def main():
     # First parse options and check if we can perform our work
     parseOptions()
@@ -1062,6 +1093,5 @@
     # And copy it to a DMG
     buildDMG()
 
-
 if __name__ == "__main__":
     main()