9100, also known 8500LE, are DX8.1 capable. 9600Se is DX9 complient. Meaning
it can do DX9 tricks in hardware, like displacement mapping, continous
tesslation etc.
However 9600SE MIGHT be somewhat better in real game performance than a
8500LE or 9100. However, if you have 9100 or 8500 in your system, then you
may want to upgrade to real 9600 (not SE). It would be much more worth the
extra money.