Loading XML Data Dynamically to Web Page

I hope this isn't too vague a question but I'm really stuck...

I have a blog in an html page that has 20 posts. All the data is held in an XML file. I want to load 10 posts per page and for there to be a 'view older posts' button that show the next 10.

I know how to load the data using XML DOM but how do I load the correct posts for each page? How does the browser know which data to load each time the button is pressed?

Hope that makes sense