The only way you could really do this using the different templates for different categories mod. Meta tags aren't all they are cracked up to be. Only a very few search engines read meta tags most of the top search engines don't. And the directories like Yahoo don't look at them either. The most important thing on your page is the page title, it should be what the page is about not your web site name or company name if you have to have your web site name in the title make it last. Limit your page title to 80 characters.The other important thing is to have the description like you would have in the meta description on the very top part of your page in plain text, it might not be what you want but it will bring search engine traffic.