for Dual Channel the"matched" memories go into slots 1 and 3 and 2 and 4. On most mobos the slots have different colors. Put two sticks in one color and you are in single channel mode. Put one stick in one color and the other stick in the corresponding other color and you are dual channel.
Again the two dual channel sticks must be of the same "size" and type.
Seems that you are actually running single channel because the pairs are not matched. Why they only run at 333 may be a problem with the quality of one of the sets of sticks.
my computer had 512mb(2x256mb) dual channel DDR400(PC3200). I decided to upgrade it to 1.5Gb. I added 2x 512mb dimms(1024mb) of the same memory. I also consulted the dell owner's manual. For some reason the old memory alone works at 400Mhz and the new memory alone works at 400Mhz but as soon as I put them together the memory only works at 333Mhz. How do I get it to work at 400mhz? I tried having dims 1 and 2 with the 512 mb dimms and dimms 3 and 4 with the two 256mb dimms an currently have dimms 1 and 2 with the 256 and dimms 3 and 4 with the 512's.
thanks in advance