actually, running far cry at the highest settings will bring down most of the best systems, being it is such a graphically intensive game at high settings, if your hell bent on upgrading now, i would upgrade the video card. If it were me, i would save up and build a 64-bit system the would put that game in its place.
my athlon xp 3200 with dual channel enabled pc3200(ddr 400, 1gb) ram with an ati radeon 9500 pro gets boggy at the highest settings.