It really depends on what capture hardware and software you were using. Sometimes you can salvage 90-95% of what you've captured, and other times the whole file is corrupt. If you're capturing to AVI in
VirtualDub, and the system either crashes (or is turned off mid-capture), or the system halts because the drive fills up, then the whole file is trash. That happens to me once in a while, when I'm not paying attention to drive space available versus what's going to be needed for the capture. A few times, I fell asleep on the studio couch while capturing -- oops -- and woke up to an error message and hours of lost work.
MPEG files are a bit more resilient, and can be salvaged in Womble MPEG Video Wizard.
Never use Ulead DVD Workshop for editing video. This would count as editing. DVDWS is authorware only.