In order to check for interlacing, it's better to use a scene with lots of motion. In any case, as far as I know DV is always interlaced. I am quite rusty in the matter as it's been a while since my last encode, but I can take a look if you want, Harmy. As a general rule of thumb, the best quality option is probably bobbing with QTGMC and then doing SelectEven() if you need to go back to the original framerate:

http://forum.doom9.org/showthread.php?t=156028

That can be quite slow, though. A good alternative would be straight-up deinterlacing using TDeint with NNEDI3, TMM and Vinverse:

http://bengal.missouri.edu/~kes25c/TMMv1.zip

http://avisynth.nl/index.php/Vinverse

Like so:

source loading and pre-deinterlacing filters
Interp = nnedi3()
Deinted=TDeint(type=1,edeint=Interp,emask=TMM())
vinverse()
rest of the filterchain

TDeint's type=1 interpolation works best on animated content, for real-life footage type=2 might be a better idea.

For even faster results, you might want to try Yadif: http://avisynth.nl/index.php/Yadif

To load the file in Avisynth, do as Chewtobacca said.