Hi,
I believe you are looking for so-called
Wildcard URLs, a new feature in version 4.0.
With this feature properly set, you could specify URL for your blog in the form:
/blog/{prettyBlogTitle}and then in the blog.aspx (i.e. the page wildcard url is set for) in code-behind, you can access the querystring field
prettyBlogTitle with the value starting behind the "...blog/" url part (e.g. "a_pretty_blog_title" according to your description).
The feature description and examples are here:
Wildcard URLs in DevGuide articleHope this is suitable for your aims.
Regards,
Zdenek C.