For instance, the blog feed URL is feeds.feedburner.com/xxx and he wants a category feed for posts labeled AJAX that should look like feeds.feedburner.com/xxx/AJAX.
Like the Category or Tag feeds in WordPress, you can also create RSS feeds in Blogger for any search label.
Here's the default URL for any search label in Blogger:
To convert that search label into a Blogger RSS feed, replace the string /search/label/ with /feeds/posts/default/-/ so the new feed URL for that search label has the following syntax:
For this to work, you should have enabled Site Feeds for that blogs. Blogger Label Feeds will inherit the full or partial text settings from the main feed itself.
Now that you know the feed address for the various search labels used in your blog, just create separate feeds for each of them in FeedBurner.
Related: Redirect Blogger RSS Feeds to FeedBurner