Every codec has more or less drastic changes in picture quality, it all depends on numerous factors, far too many if you don't know how it all works.
WMV video can have the same picture quality, but this will cost you a must larger filesize in order to deliver you a video file that can be edited in WLMM. However, if you have enough patience, you can convert this MOV file to a large WMV file, edit it in WLMM and recompress it for uploading.
Googling resulted in a few MOV editors which have been dropped from development and probably can't provide satisfying results because the codecs always improve, but as far as converter and encoder software goes, you can try MediaCoder
. This app is very useful, but also very detailed, so if you really want to step into the world of editing and encoding, you're gonna have to learn a lot.