s running multple sound devices

I use a program called Virtual DJ for, well, dj'ing. My setup utilizes two external soundcards/controllers which are run simultaneously for mixing tracks. On windows xp this works perfectly,but run under vista, the tracks skip ahead randomly. This is without high cpu usage or i/o activity. This does not happen if i remove the controllers and use the internal soundcard (which is not an acceptable solution). Can anyone offer some feedback on how to stabalize the audio ?