According to
http://help.godaddy.com/article/899, GoDaddy supports mod_rewrite.. The lines in your .htaccess, are they wrapping in TextEdit? Because each rule should be on one line by itself, in case something got messed up when copy-and-pasting??
You could also try just the top 2 lines in .htaccess only (as a test)
Code:
RewriteEngine On
RewriteBase /Portfolio
and see if you get any internal errors. if not, then you messed up copying one of the rules over. It might be easiest to copy them from the README.txt file included in the download ZIP file.