if you want it running down a cheek or something, i think that might be a lot easier to do with a compositing program than in 3d... just film footage of a tear running down a cheek, then using an animated mask, change the color to redder than usual. if you want it falling in mid-air, then gster's got it, but you don't need to really import footage into maya, just create your teardrop animation, and place the the resulting footage wherever you need it to go. being able to move footage around on your composition makes things nice and easy, instead of importing footage and trying to match it up.