I am also posting this with SP2 (and the firewall on) and htmlArea without difficulty. However, there may be other security settings in IE that are restricting you from using htmlEdit. I'd try going to tools->Internet Options->Security. Click on the "Trusted Sites" zone. Add the moodle sites you visit to that zone, and set the security settings for that zone to the Default->Low setting.
Best wishes,
--Rudy