How do you mean the only music you can get is from WMP?
You should just be able to click on the "Add" button and add whatever files you want. This is Nero Express in the first two screenshots, then the more advanced Nero Burning ROM which is essentially the same thing but with more bells and whistles. I prefer Express because it's more lightweight.
For your other questions...
Different skins and backgrounds I haven't messed with too much, and I'm assuming you mean for StartSmart. Unfortunately it's not too flexible, but you can try changing some of these options...
Haven't done anything with web radio, so I wouldn't know how that works.
Nero Home looks like quite a decent media centre..? But again I haven't played with it too much. I'm not exactly a Nero expert.
