Where can I find out about performance for mySQL stuff? I just have general questions about how to organize my tables and such. Like, is it better to have one big table with all your news? Or separate tables by category? Will a search be faster by searching one big table, or four separate tables?
Testing is the only way that you're going to find an answer to most of these questions. The results depend heavily on your own unique usage situation. Discover which data views or modifications will be requested most often and optimize your database design to speed access for those queries. Data retrieval speeds can be greatly improved by creating indexes for the keys most commonly searched. For more information on creating indexes in MySQL see this tutorial.
As long as the columns will be the same for each category, it would be best to just put it all in one table. It is much more difficult (and slower) to do a search on four seperate tables and combine the results than to just search a single table. It will also be a lot easier to maintain if you use only one table.