This is a very confusing time for understanding streaming laws for music on the internet. EMI has sued Grooveshark, but so far nothing has come of it, but it's entirely possible that Grooveshark will go the way of Muxtape - that is, kaputt. And that's despite the fact that they've worked out agreements with other record labels and performance rights organizations.

But really, you're uploading a single song that can be streamed on your blog. I'm not sure how legal it is, but the chances of getting in trouble for it are minuscule. At the very worst, you'll be contacted by the artist or representative asking you to take it down per the digital millennium copyright act. But more likely, no one will ever take notice of it because you're not heavily impacting the artist whose song you'd like to upload. The chances of it being removed climb if the artist is signed to one of the major labels, I believe EMI is particularly vigilant about music streaming.

The problem is that this artist will get no royalties from their music being played. Maybe if you're wildly lucky, your blog is hosted on a website that has some kind of contract with SoundExchange, which I believe would cover you as they assess royalties based on internet streaming, though they only deal with internet radio as far as I know.

So, basically, if I were you and this was a song from an unsigned or indie label artist who could use any bit of exposure, host it. If it's a song from a band or artist already signed to a major label, don't risk it.