HELP ME PLS.. I AM A NEWBIE

I got an ECS K7S5A with AMD XP1700+. I used ELIXIR DDR RAM.
in the CPU setting, there is only 2 choice fro me to choose the CPU speed 100Mhz and 133. So i choose 133 rite even though the ram is PC2100. It is not stable when i first use PC133 and set the CPU speed to 133, only work for 100 so i decide to change to DDR ram instead. Maybe this board don't like SDR. I don't overclock and I just try to get advice for the best seting for my syst. Is the setting rite with 133?? because i read there some people have setting up to 166, but my board has only 2 opts. 100 or 133..?
and anyone know is this RAM good with the board, I was told by the salesperson that for this board, this ELIXIR ram work same as AZEN or CRUCIAL. and to get the best setting for this board on the bios what should i put for the speed of ram such as 2T, 3T, or SPD
and for time setting mode.. should i choose Normal, Ultra, or Safe.
anyway I very new and slow, anyone has experience with this board pls tell me your setting and which RAM to do to get the best . by the way I am using winXP and do I need to upgrade the bios? my current bios is V1.0
thank you so much to all