There is one MKV to AVI converter I know: http://freemkvtoaviconverter.com/
It's free and rather easy to use however converting process may take a very long time depending on the video duration. I waited for about 2 hours to change the format of a movie once but the I was said that was pretty much normal.
To burn mkv files to a disk I would most likely use the last version of Nero which is unfortunately a paid tool or BurnAware which is free.