i’ve been workin on video edit project in 2.53 VSE
it was useable relatively
but unstable (crash when undo…losing key datas…)
so, update it to 2.56 recently
but everything gets slow
i can’t scrub audio and play in realtime
plz help
Its Beta, what are ya gunna do… log bugs in bug-tracker 
Go to the timeline window menu–>playback and make sure that audio scrubbing is checked and audio muted is not.
Then you might want to enable avsynch and framedropping, both might help with smoother playback --though framedropping might off course skip frames to keep up with the audio.
If the above steps don’t help, then you could go to the user preferences–>system and change the sound system. That might help with the audio playback. Finally, you could set the number of prefetch frames in the sequencer panel to its highest value (500).
Out of curiosity: what is your OS and what is the resolution of the video you’re importing for playback?
thanks for ur reply
i’m handling half HD 720p(1280 x 720)
tga image sequences
in windows xp 32bit
Blender’s VSE is very fast with image sequences because the frames are arealy available and need not be computed in real time which causes lags. Most of what I’ve suggested above does not actually apply if you’re using sequences. I use pngs (and to a lesser extent jpegs) all the time. Dunno about tga files though and 720p should definately be doable. On my system video playback with stills is pretty smooth (32bit, intel dual core cpu@ with 4GB ram, ext4 filesystem).