You've probably finished your research on this topic by now but...
For music videos and the like, the 7D is a much better way to go than a regular video camera, even one like the HVX 200 - although with a Letus Ultimate and some decent lenses it's quite remarkable. I bought the 7D over a month ago and I've already shot a couple spots and a "film" for the UN with it. As for glass - I adapted my Nikons with the Kawamall adapters and and that works great, but I also got an L-series lens and I'd recommend getting this over the less expensive ones, simply because if you are serious about this as a career, it won't be long that you'll find you're ready for the next big thing, the new 5D or 1D or whatever and you'll already have your lenses and support gear (still waiting on my back-ordered z-finder, but something like that is going to be crucial as well). Tom is right in that those cheaper lenses are good, but they won't work on a 5D.
There are many arguments for not buying a camera but the sooner you get one in your hands and start experimenting with it and learning things, the quicker you'll learn about cinematography-and the better you'll become. There are so many ways that this camera functions like a film camera, not an HDV video camera and I think that is a big plus.