Writing articles that have "formatting" in a word processor of any kind is a problem when you copy and paste to just about any browser to any web page based CMS like WordPress.
Microsoft Word is the worst. Open Office is much better, but still will cause you problems if you've done a lot of formatting in your article.
If you MUST copy and paste "formatted" material, than make sure you're on the "Visual" tab in your WordPress editor and use the "Paste from Word" or "Paste as plain text" buttons.
Then, as Saildude suggested, do you formatting in WordPress.
Another alternative is to use an HTML editor like "Trllian Webpage" - it free - not the best, but works.
You can copy and paste to Trillian and then click on the source tab and copy the actual HTML code. Goto your WordPress editior and click on the "HTML" tab and paste the HTML source into WordPress.
You'll probably find some formating issues that don't paste over 100%, but it will get you close.
I personally tend to write all my articles using Open Office with little or no formatting (wait until I paste it to WordPress)
The only time I use Trillian is when I have a complex table that I want to create and want more control over the HTML code in the table.
Hope that helps