I've been trying to do similar with my GeForce3 and my XBox... I haven't found any free software that will work yet. Asus' DVR Software works, but it's quality sucks.
DScaler is apparently one of the best programs, but it only works with Connexant chipsets, which is definately not what my GeForce3 uses... I haven't a clue about the GeForce4, but I would bet it's similar to the 3.
Sorry I could be of much help, but I'm hoping someone else could be... I don't want to have to buy the ATI TV card I've been looking at for the past week....