Tell us more about your system. What OS, version of FCP, kind of drive and type of connection, etc. If both your drive and camera are connected at the same time to your Firewire bus, that could be your problem as Macs have only one FW bus regardless of how many FW ports are on the machine. A slow drive could also cause dropped frames, but usually not a second’s worth at a time.
John
MacPro 8-core 2.8GHz 8 GB RAM OS 10.5.5 QT7.5.5 Kona 3 Dual Cinema 23 ATI Radeon HD 3870
ATTO ExpressSAS R380 RAID Adapter, PDE Enclosure with 8-drive 6TB RAID 5
24″ TV-Logic Monitor
Final Cut Studio 2 (up to date)
Pro Tools HD w SYNC IO, Yamaha DM1000, Millennia Media HV-3C, Neumann U87, Schoeps Mk41 mics, Genelec Monitors, PrimaLT ISDN