aptitude install firmware-linux-nonfree
My Wi-Fi card also required firmware, which I found in Add/Remove Software. (Yes, the same Wi-Fi card that was blocking my installation.)
But I could play MP3s out of the box and most of my videos too, with the exception of .mp4 files, which don't play because of a regression in a library which should be fixed soon.
Who said Debian is difficult? OK. I might need to add Adobe Flash from Add/Remove Software if I really want to watch BBC news or tubes, but I have a usable system pretty much out of the box, and good looking too. (Yes, I like Gnome 3.)
So the things to do after installing Wheezy are to install your video and Wi-Fi card firmware.
In my next post I'll look at some of what I think is the most essential software to add to Wheezy, although still in minimalist mode.