Firstly I would be unimpressed with a DVD authoring company that requests DV tape. It is not a good codec to then create an mpeg2 file from for a DVD.
As for the process of doing a standards conversion, the basic rule of thumb for me is to start with the native resolution either on tape or as a QT file and find a facility that has a quality hardware down/standards conversion (like Teranex)to make a digi beta tape or uncompressed QT file in PAL (720 x 576 anamorphic).
If the company in France can’t accept digi beta or uncompresssed QT file, then I suggest you take the file back into Compressor and make the mpeg2 file for them. There are lots of useful presets in Compressor and there have been tons of posts here at the COW about getting a good result so a quick search will unlock heaps of opinion and advice.