Support for SSE3 instructions — The Venice core can execute 11 of the 13 instructions that make up SSE3. Pioneered by Intel in its Pentium 4 "Prescott" chips, these 11 instructions are targeted at speeding up certain types of computation. Five of them are aimed at complex math operations like fast Fourier transforms (often used in scientific computing), while another four allow for better data organization in software vertex shader routines for graphics. The handful of others should improve performance in video encoding and speed up conversion of float-point data types to integers. The two SSE3 instructions that the Venice core doesn't support have to do with thread synchronization for Hyper-Threading and simply don't apply here.
from http://techreport.com/reviews/2005q2/athlon64-venice/index.x?pg=1