Avoid the default FC's de-interlacer filter.
You have two good options for FC: Re-Vision Fields-Kit, and Nattress.
There is a free application called Jes-deinterlacer, that seems to do a very good job. I've never tried my self.
You can also try MPGStreamclip and Compressor.
All those plugins and applications have few de-inerlacing options (no really MPGStreamclip, but works well). Depending on your footage, you may need to use one or another and tweak the presets.