I've a Leadtek A280 LE VIVO card (Ti 4200 8x), but cannot get the video capture to work despite trying several WDM driver versions (both Leadtek and nVidia) and different card drivers too. I've tried the card on two motherboards - Intel 815 (Win ME/2000) and Asus A7N8X Deluxe (Win XP).
Look around and try the 1.08 WMD drivers. I had problems when inputting videos from a VCR ( a white band appeared in the captured video during playback). That version solved the probs. Befor installing the drivers make sure you get rid of all four devices in the device manager (they're all identified as WDM (capture, audio crowbar...).
hope this solves it. Oh yeah I have since tried the WDM ver 1.22 from Nvidia but the same white band appears.