I use Bulletproof Security plugin, so the .htaccess file is quite robust. I can post its contents here if you think it would be of trouble-shooting value.
The WP installs are on:
http://artwpn.com (should redirect via htaccess to http://blog.artwpn.com, but just gives a 403 Forbidden error)
EDIT: I fixed it. I am embarrassed to even admit what it was… changed my DB settings and never updated the config files! DOH!