Hello,
I can do that script, similar to one I wrote for my project - http://sosacek.info. It show some errors, because there are not set texts. It is very easy script, supports nice filenames, and you can download UP TO 9 formats (but only FLV, MP4 and 3GP which YouTube serves). Easy to customize ads.
EDIT: Uh, I must write, that my script DOES NOT CONVERT on server, it just use files provided by YouTube.