I'm pretty sure hardware acceleration for flash on Linux never really materialized. The nvidia card hardware acceleration works well on Linux with the nvidia binary drivers for non-flash video. As waterhead said, flash video on Linux is best done with a speedy CPU which your mobo doesn't have.
Personally I just avoid flash video - about the only thing I'll watch flash-based is HBOGo, and it's only in our theater that has a quad-core PC so it works well. The other Internet video I watch are either feeds from places like revisions3, twit, Nasa etc which tend to be mpeg4 (so they play well with the nvidia driver) or I stream a Roku locally on my network for everything else (netflix, amazon, etc). I'm a DirecTV customer and they will not allow HBOGo on the Roku - but on a PC it's OK. They must figure the Roku is just to easy for the average Joe to use while a HTPC isn't, so they allow it's use.