I think that the main prob here is the CPU: a P4 1.6 ghz is not average, it's really an old processor (heck, I use an AMD 2.5 ghz and's been out of production for a while now) - the graphic processor of the card is of secondary importance IMHO... and for obtaining good renders it's cheap upgrading the cpu that going for a new video card. Besides, it's almost useless to choose render settings above broadcast with GR enabled 'cos is simply overkill.