I'd have thought Ubuntu has the broadest and most helpful online community. It's not my choice of Linux though. I find OpenSuse easier especially with Yast, plus I prefer the KDE desktop (and unlike Ubuntu/Kubuntu[which I think is poor], you can install both desktops plus others on one system)... I think the official KDE support forum is a bit "serious" though.

Really, with Linux though, I think you are best of trying a few to find out which distro works best for you.

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As for the sound, I've a feeling flash can get in the way and block sound for other programs and it's not clear to me how the browser plugin is configured. It's working for me with other apps atm but I have had problems in the past... I think one possibility might be to install pulse audio but I'm unsure..