Hi, download Apples own FireWireSDK26 (free from Apples developer site, apple.com/developer - just register or use your .mac address) this has a great app in this SDK called DVHSCap which will capture your stream as you play it on your cam in real time and you'll be able to open that stream with Mpeg Streamclip (
www.squared5.com - another great free app) and convert to whatever you'd like for editing ie: .DV etc.
Sorry I just re-read your post, you're using USB so you won't need the FirewireSDK hopefully just mpeg streamclip.
Here's a little info from mpeg streamclip which may help you, good luck hope you manage to sort it.
OTHER COMPATIBLE DEVICES
MPEG Streamclip is compatible with FireWire, Ethernet, USB and DVD devices like Elgato EyeTV digital video recorders, ReplayTV digital video recorders, the Humax PVR-8000 set-top box, the Homecast set-top boxes, the Technisat S1 set-top box, the Panasonic SV-AV100 camcorder, the JVC Everio camcorder, the Sony T1 camera, the Panasonic VDR-M70 and the Hitachi DZ-MV230 camcorders; and with many other devices.
MPEG Streamclip is also compatible with MPEG-2 devices supported by DVHSCap and VirtualDVHS (free applications available from Apple as part of the FireWire SDK for developers); namely, the Sony IP7/MicroMV, the Sony HDR-FX1, the JVC GR-HD1 camcorders; the JVC HM-DH30000U and the Mitsubishi HD-2000U video cassette recorders; the Samsung SIR-T165 set-top box, and many more cameras or recorders. If you have one of these devices, please connect it to the FireWire, use DVHSCap or VirtualDVHS (whichever works better) to capture the M2T file, then use MPEG Streamclip to convert the M2T file into a more useful format.
Of course, a complete list of compatible devices is not possible since MPEG Streamclip can work with a wide range of MPEG devices and recorders. However, all known compatible devices have been listed here.
If you have a DVD and you want to play or convert its content, please open one or more VOB files from the VIDEO_TS folder.