If you want to do it by yourself, you can implement an observer, check which filters are applied in the layered navigation and add your block to the content block.
Your block then implements whatever logic you want to show the different informations for the manufacturer.
I would try controller_action_layout_generate_blocks_after, controller_action_layout_render_before or controller_action_layout_render_before_'.$this->getFullActionName() whatever the FullActionName for the layered category is :-)
About Observers you can find things at inchoos: http://inchoo.net/category/ecommerce/magento/events-observers/
To get the information wether a manufactuerer is choosen, I think there are two ways:
- get the information from the get
Mage::app()->getRequest()->getParam() should work
- get the layout, then
$layout->getBlock('catalog.leftnav') and pull the information somehow out of the block
afterwards you can add your block.
After reading this: Magento: Add content block at the end of the structual block "content"
I would suggest to introduce your own update handle (because I don't know, how to prepend blocks to the beginning of content). with your own handle, you can use before="-"
And as described here:
http://www.classyllama.com/magento/add-custom-layout-handles-e-g-parent-categories
you can add your handle via $layout->getUpdate()->addHandle('manufacturer_informations');
I would try something like this in the observer:
if($category = Mage::registry('current_category')) {
if($category->getName() == 'MyBrand') { // ot maybe $category->getId() == ...
//instantiate some $block
}
$layout->getBlock('content')->insert($block, 'brand-information');
}