Vista not 'capturing' video frames fluently!

Hey guys, I am having this strange problem in Windows Vista, when trying to capture video using my new EasyCAP USB Video Capturing Adapter. Video Capture video preview is very smooth in Windows XP, under all programs, but in Vista, the video preview is very slow. You see the frame change like once in every 10-15 seconds! Sometimes there is no video feed at all !!! What could be the problem here ?