Vista is loaded with traps that prevent users from recording (pirating ?) video for which they do not hold the copyright. This is mainly to prevent people copying and distributing High Definition video from the new formats such as BluRay and HD-DVD. Vista will degrade quality and actually prevent capture and playback of any video stream it suspects is copyrighted. Another problem is that Vista's Aero graphical interface hijacks the video overlay usually used to present video on the screen. Unfortunately, video software not written specifically for Vista will get clobbered by Vista one way or another.
I assume you are using Premiere Pro 1.5 or 2, so if you can possibly afford the £250 or so to upgrade to Premiere CS3 when it comes out in July, you will find that not only will everythiing work properly in Vista again, but you will also have the heavyweight DVD authoring program Encore and the real-time capture utility OnLocation included in the price.