Here are the links to download GoAsm and the other "Go" tools, and the main links to help and support:
GoTools download page (http://www.godevtool.com/)
Compendium of tutorials and sample code (http://www.masm32.com/board/index.php?topic=7288.0)
Donkey's Stable (containing lots of sample code, header files etc) (http://www.quickersoft.com/donkey/index.html)
Wayne J Radburn's GoAsm examples and programming tools (http://www.magma.ca/~wjr/)