I just captured my first dv footage on Vegas 9 and it dropped 501 frames in 60 minutes of footage. I am capturing from a dvx100b thru the 1394 ohci compliant host controller jack on the motherboard of a Dell studio xps 8000 2.8g i7 machine; do I need to install a seperate IEEE 1394 capture card?
Were you capturing to a separate hard drive or the same hard drive that Windows is on (i.e., C:)? Do you have a permanent swap file set up? 501 is a lot of frames to be dropping but I would be sure that the rest of your system is set up correctly before you buy another firewire card. I capture with the firewire built into my motherboard all the time and I never get dropped frames.
Also, just for troubleshooting, try disabling any antivirus during the capture. You may also want to ensure that you don't have a bunch of background programs running that are not needed. (you can disable them by going to start/run/ and type in msconfig. There should be a tab called startup. You can uncheck everything that you don't want running (or don't need running).
...and depending on which OS you are using, check the Device Manager to see if the firewire device is also being used as a network adapter. If it is, disable that network adapter. This particularly important to check on XP.