We REAAAALLLLY need to make a sticky post in this forum that very clearly tells people not to expect smooth playback of native files on their computer (I know this is touched on in one of them, but this needs to be in the thread title, so they'll read it). This is the most common thread topic that appears on this forum
The sum up: Everybody has totally crappy playback of native files, they're a nightmare to work with in anything but CS5, yada yada yada.
I convert with Neoscene before attempting any editing. Will attest to its goodness.
Don't mean to sound snarky, just so many threads on the same... thing... over... and over.
Write it up, add some links, format it nicely, post it as a new thread, then report it asking for it be made a sticky
A mod will see it, and, its it up to standard sticky it for you