i know nothing about flexi... but don't you need the mimaki firewire driver cd? if you do this cd is a pain in the ass for some service paks of xp. you have to tell it "no, i don't want to restart my computer"...then it does the whole thing over again.... it's detailed out in the read me. but it is a very sloppy install. basically installs two separate things in a row. also, in the rasterlink printer management (which you probably don't need, or maybe you do. i really am no that knowledgeable about rips and such), you have to choose each item in the exact order explained in the manual. even though it doesn't specify doing it in an order (like step one, step two, etc). my print manager will not find my printer unless it is and exact order even though i'm just choosing preferences in a single non-linear window.
i doubt that helps. tomorrow there will be scores of really smart guys that use flexi/jv3's and will probably solve your issue in a single sentence.