To have Wordpress empower your website takes a fair bit of effort, and some PHP file fiddling. For future reference you might want to invest in the following: http://rockablepress.com/launch/building-wordpress-themes-from-scratch/
Wordpress would be overkill for simple messages as it really is a full grown CMS that you would typically have manage everything or work as a seperate entity.
Textpattern (http://textpattern.com/) is a lot simpler, quicker and lightweight, again it's a complete solution but for future reference it might pay you to read up about it.
If you are after a quick solution to dynamically add content to your website, i.e login to admin area and change the text of a page or section. May I suggest Simple CMS (http://www.phpjabbers.com/simple-cms/) It's not really a blog but you can use it to update a News page by re-editing the text field. It's quick and cheap.
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Actually, it seems that the Simple CMS people also do a blog script (http://www.phpjabbers.com/stiva-blog-script/) "With just a few clicks you can have a PHP blog software integrated into any website or software system" - That might be the answer you're looking for.
Hope that helps!