Well, the way it looks to me is, go with T&L.
Most of the newer games will be inclusing T&L support, and, if you use Open-GL it can increase your systems performance drastically.
T&L stands for transform and lighting, both of which are done by your CPU. The new cards with T&L engines will take most of the strain from doing this, off of your CPU, whereas monster cards, like the upcoming Voodoos' will still only provide pure power, which is good, for programs with high polygon counts. But cards like the GeForce256 and the upcoming card from ATI will be better. They will be strong and they will have T&L engines, so, in other words they will be the best of both worlds.