From what I know is that:
If you OWN the album/song you're downloading, then download to your heart's content.
You've already made the purchase-- it's yours. Just don't SHARE the damned thing with anybody. "They're" after the DEALERS not the users.
Limewire is cool... I'm told... especially when you're looking for a tune that one of your company's stations may already own, technically.
The question is not so much where you get the songs, but are you allowed to legally use them in a spot?
Let's say all those bar commercials with every stoopid teenie-bop under the sun.... are THEY paying royalties to use that? Whether it's an overall ASCAP/BMI fee, or by song? I'll bet Cadillac didn't just take a show of hands whether to use "Rock & Roll" from Zeppelin. They had to spend MUCHO bucks. And why shouldn't they?