Hey, sorry to hear that. It's extremely frustrating!!!
Here's what I've learned since and it's made a huge difference for me.
First, make sure you have enough ram. It makes a big difference when you're editing movies.
Second, work with the task manager loaded up so you can see how hard your processor is working. I'm not sure what it's like in Vista, but in XP you can load it up (cntrl+alt+delete) and then minimize it and it'll show you whether your processor is working at it's max or not.
NOTE: One of the reasons (from what I've found) for broken files is that I would start having trouble so I'd hit "Save" and it would save it in it's "trouble" state and I'd have a broken file. Save your file only when your processor isn't struggling to keep up and when you're not in the middle of an action.
Third, never save the same movie under the same file name--ever. This will seem extreme at first, but this alone may save you the trouble of broken files.
Someone suggested that I save a second copy of the file, but I find that this works better. For example: Start your file and save it as "Movie 01.pds" When you do some work on it, save it again as "Movie 02.pds" When you do some more work, save it as "Movie 03.pds". What this does is it ensures that the most you will ever lose is up until your last save--unless, of course, it's messed up from the beginning...
. Since I've started doing this, I've had little to no problems. If I have trouble loading up "Movie 17.pds", I can always go back and load up "Movie 16.pds" or "15" and I've lost hardly anything. A little extra work and it's saved me a lot of anguish.
That should save you running into this problem. For your files that are lost... I'm not sure there's any hope. I don't even want to think back to the files I've lost... it brings up bad feelings.
Hopefully this will save you experiencing it anymore.
Shawn