There is a huge bug with wordpress where you can't post in IE7 unless on your main options page you type www. for your blog url so http://mysite.whatver makes it so you can't post anything and you have to type http://www.mysite.whatever to post anything using IE7. Alot of people have posted problems relating to thise one bug, and they have tried a ton of different things but obviously the solution is to fix this one simple issue.
Here are some suggestions to fix it.
1.Automatically make that field not work unless www. is there.
2.Change it automatically.
3.Make sure wordpress always installs with the url http://www.yoursite.whatever unless it is a subdomain of course.