Dynamic content in a post/page?

On my weblog, I have a page called “goals for 2009”, showing a list of various things that I want to do during this year. One of those things is that I want to read at least 75 books.

I have a category where I write a book review every time I finish reading a book, and I thought that it would be nice to simply use the post count in this category to show how close I am to my goal.

Then I discovered that there seems to be no good way of doing this. How would I best write a page where one of the lines is:

Read 75 books. Progress: <amount_of_posts_in_category_”Books”>/75.

… because I can’t figure it out.