Joomla and then WordPress

Hello. I have running fully functional Joomla on http://www.mediapress.hr However to save the articles, i need to keep it cause i dont want to use big prices conventers. my question is: how to install WP without losing already posted articles using Joomla. So when i install WP i can still access database of old Joomla articles with their design and layout, and when operating with new articles, so that they use WP design from where they were created Did i complicated it too much? Simple: I want to use WP and be able to access old articles created with Joomla!