There is no built-in deinterlacing in MC, but you can use deinterlacing functionality in DirectShow filters. There are two obvious options that I can think of:
1. Use FFDShow. FFDShow Video decoder filter has deinterlacing functions in it. If your file type does not use FFDShow video decoder, you can add FFDShow Raw video fitlter.
2. Use Deinterlace Filter. This filter is installed with MC for TV purposes, but may also work with certain video playback.