How are you capturing, setting up, etc?
Are you using a tape deck to capture, firewire to capture, plugging in through USB/Firewire (it pops up as a device), using a SD card, or any other way I haven't listed here?
Are you using FCP or FCE (express or pro). Are your settings correct in Easy Setup. What are your computer's specs like RAM, processor, etc? These things all could affect your capturing.