Render as QT:Animation. Set to RGB+alpha. Make sure its millions +. Plus means it has alpha. Depends on edit system, but you sahould probably change to straight.
To cover your butt, you could also do a version set to premultiplied. And if you really want to cover yourself, you could do another version set to just alpha, and they could use that as matte.
I know avid requires straight, so that's what i mentioned; what i deliver to.
They want the sequence rendered out as a tiff sequence not a quicktime movie...
it can be done also with alpha, tga, tiff, png sequence
Tiff sequence supports alpha channel. All you have to do is to set the color mode to RGB + Alpha and then set the alpha channel as premultiplied.
Then you'll just have to hit render and take a cup of coffee.
To include an alpha with .tga, you also need to also go into format options and set it to 32bit. Probably need to do that with .tif as well.
FYI. 32bit = RGBA (4 channels) * 8bpc (bits per channel)
You need to know what program you're sending it to, and need to know whether it supports premultiplied alphas.. For instance, Photoshop and Avid edit systems can only use straight alphas.. If you import a premultipled alpha into these programs, you will see "halo" around your object.