Yahoo Pipes, filter by item.category.
Expanding: Yahoo Pipes allows you to create custom RSS. For this question, you simply put your blog RSS as source. Then you add a filter that allows only items of one category (something like this: http://pipes.yahoo.com/pipes/pipe.edit?_id=6b44f0135bde67b74a8561ba4a06747c). Use the output as the RSS for that category. Repeat as necesary. Hope is more clear now.
