ESPN3 is technically WatchESPN.com, now.
It's not difficult. You just log in through your service provider.
If you have a solid internet connection, it will be a quality HD stream. However, running it from your laptop to your TV, the quality will mainly depend on the cord you're using. I have a mac-to-HDMI converter that isn't great. My buddy bought a more expensive one and it was definitely worth the extra $.
Either way, you'll be good.
I use something like this, and run the HDMI cord from it to the TV:
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"I don't get sick. I don't observe major holidays. I'm a jackhammer." - Jim Harbaugh & Dwight Schrute