When configuring Layred Navigation you will find that for this to work you need the categories to be set as "Is Anchor = Yes" but if all your categories are set to No this can be very time consuming. The articles in this category will show you how to global change this setting.

nileco.com/change-categories-magento-anchor-yes-1-click/
Often times there is a need to change all Magento Categories from their default setting of ‘Is Anchor = No’ to ‘Is Anchor=Yes’. Making the change to an Anchor Category activates the Layered Navigation, also known as filtered nav ...

magento.stackexchange.com/questions/3531/how-to-apply-a-cate...
I have many categories and instead of applying new settings to all categories one by one, i would like to know if this is possible to apply new settings to all categories at once?
This thread will show you how to use SQL to change all of the ca ...

joshpennington.com/set-all-your-magento-categories-to-is_anc...
I recently was tasked to set every category inside our Magento installation have its is_anchor attribute set to true. We have over 600 categories so it would be a huge task to do this by hand so I put together a quick script that did this in less than ...