diff --git a/SkeinPyPy/skeinforge_application/skeinforge.py b/SkeinPyPy/skeinforge_application/skeinforge.py
index 33279a9..9afb64e 100755
--- a/SkeinPyPy/skeinforge_application/skeinforge.py
+++ b/SkeinPyPy/skeinforge_application/skeinforge.py
@@ -579,6 +579,14 @@ class SkeinforgeRepository:
 		self.executeTitle = 'Skeinforge a file...'
 	
 	def getPyPyExe(self):
+		if platform.system() == "Windows":
+			checkSSE2exe = os.path.dirname(os.path.abspath(__file__)) + "/checkSSE2.exe"
+			if os.path.exists(checkSSE2exe):
+				if subprocess.call(checkSSE2exe) != 0:
+					print "*****************************************************"
+					print "* Your CPU is lacking SSE2 support, cannot use PyPy *"
+					print "*****************************************************"
+					return False
 		if platform.system() == "Windows":
 			pypyExe = os.path.normpath(os.path.join(os.path.dirname(os.path.abspath(__file__)), "../../pypy/pypy.exe"));
 		else:
diff --git a/SkeinPyPy_NewUI/newui/skeinRun.py b/SkeinPyPy_NewUI/newui/skeinRun.py
index bd1c3c9..306d56c 100644
--- a/SkeinPyPy_NewUI/newui/skeinRun.py
+++ b/SkeinPyPy_NewUI/newui/skeinRun.py
@@ -6,6 +6,14 @@ from skeinforge_application.skeinforge_utilities import skeinforge_craft
 
 def getPyPyExe():
 	"Return the path to the pypy executable if we can find it. Else return False"
+	if platform.system() == "Windows":
+		checkSSE2exe = os.path.dirname(os.path.abspath(__file__)) + "/checkSSE2.exe"
+		if os.path.exists(checkSSE2exe):
+			if subprocess.call(checkSSE2exe) != 0:
+				print "*****************************************************"
+				print "* Your CPU is lacking SSE2 support, cannot use PyPy *"
+				print "*****************************************************"
+				return False
 	if platform.system() == "Windows":
 		pypyExe = os.path.normpath(os.path.join(os.path.dirname(os.path.abspath(__file__)), "../../pypy/pypy.exe"));
 	else:
diff --git a/build.sh b/build.sh
index 675b5b8..358c743 100755
--- a/build.sh
+++ b/build.sh
@@ -1,5 +1,8 @@
 #!/bin/bash
 
+# This script is to build the SkeinPyPy package for Windows/Linux and OSx
+# This script should run under Linux and OSx, as well as Windows with Cygwin.
+
 #############################
 # CONFIGURATION
 #############################
@@ -96,6 +99,16 @@ if [ $BUILD_TARGET = "win32" ]; then
 	mv PURELIB/serial ${TARGET_DIR}/python/Lib
 	rm -rf \$_OUTDIR
 	rm -rf PURELIB
+	
+	#Clean up portable python a bit, to keep the package size down.
+	rm -rf ${TARGET_DIR}/python/PyScripter.*
+	rm -rf ${TARGET_DIR}/python/Doc
+	rm -rf ${TARGET_DIR}/python/locale
+	#rm -rf ${TARGET_DIR}/python/tcl
+	rm -rf ${TARGET_DIR}/python/Lib/test
+	rm -rf ${TARGET_DIR}/python/Lib/distutils
+	rm -rf ${TARGET_DIR}/python/Lib/site-packages/wx-2.8-msw-unicode/wx/tools
+	rm -rf ${TARGET_DIR}/python/Lib/site-packages/wx-2.8-msw-unicode/wx/locale
 fi
 
 #Extract pypy
@@ -106,10 +119,22 @@ else
 	cd ${TARGET_DIR}; $TAR -xjf ../pypy-${PYPY_VERSION}-${BUILD_TARGET}.tar.bz2; cd ..
 	mv ${TARGET_DIR}/pypy-${PYPY_VERSION} ${TARGET_DIR}/pypy
 fi
+#Cleanup pypy
+rm -rf ${TARGET_DIR}/pypy/lib-python/2.7/test
 
 #add Skeinforge
 cp -a SkeinPyPy ${TARGET_DIR}/SkeinPyPy
 
+#Add the SSE2 check if we can build it, else we skip it.
+#  If we don't have it SkeinPyPy will still function. But crash on machines that don't have SSE2
+if [ $BUILD_TARGET = "win32" ]; then
+	WINCC=`whereis i386-mingw32-gcc`
+	if [ "$WINCC" != "" ]; then
+		make -C checkSSE2 CC=${WINCC} TARGET=checkSSE2.exe
+		cp checkSSE2/checkSSE2.exe ${TARGET_DIR}/SkeinPyPy
+	fi
+fi
+
 #add printrun
 mv Printrun ${TARGET_DIR}/Printrun
 
@@ -122,6 +147,7 @@ cp README ${TARGET_DIR}/README.txt
 #package the result
 if (( ${ARCHIVE_FOR_DISTRIBUTION} )); then
 	if [ $BUILD_TARGET = "win32" ]; then
+		rm ${TARGET_DIR}.zip
 		cd ${TARGET_DIR}
 		7z a ../${TARGET_DIR}.zip *
 		cd ..
diff --git a/checkSSE2/Makefile b/checkSSE2/Makefile
new file mode 100644
index 0000000..02d7b57
--- /dev/null
+++ b/checkSSE2/Makefile
@@ -0,0 +1,6 @@
+CC ?= gcc
+TARGET ?= checkSSE2
+
+$(TARGET): main.c
+	$(CC) -o $(TARGET) main.c -Os
+
diff --git a/checkSSE2/main.c b/checkSSE2/main.c
new file mode 100644
index 0000000..9c66aa9
--- /dev/null
+++ b/checkSSE2/main.c
@@ -0,0 +1,21 @@
+#include <stdlib.h>
+#include <stdio.h>
+
+//Read CPU flags, and return 0 if we support SSE2, else return 1
+//See: http://en.wikipedia.org/wiki/CPUID#EAX.3D1:_Processor_Info_and_Feature_Bits
+
+int main(int argc, char** argv)
+{
+	int features;
+	
+	//Read the CPU features.
+	asm("mov $1, %%eax\n"
+		"cpuid\n"
+		"mov %%edx, %0"
+		: "=r"(features) : : "%eax", "%edx", "%ecx");
+	
+	//Check bit 26, this indicates SSE2 support
+	if (features & (1 << 26))
+		return 0;
+	return 1;
+}
\ No newline at end of file