Yup you will run single channel mode if the motherboard doesn't support DC. The system will be slower than a similar system that supports DC but it'll be very minor- I don't think you will notice it.
And yup DDR memory will support both dual and single channel no prob. Happy new year!
I am working on a Dell deminsion 8400. The computer has four slots and can support 4 GB of memory. I am not sure if it can use dual channel memory or not. I was at the Newegg site and the crucial configurator indicates that I can use the dual channel sticks. However, when I visit Crucial's web site directly and use thier configurator I am not offered dual channel as a option.
My question is, does the dual channel memory operate on single channel mode if the motherboard does not support the dual channel. And if so, does the system slow down because I am using dual channel on a computer that does not support dual channel mode?
I am also asking in general, if it is true for all systems that the dual channel memory will work for any motherboard and switch back to single channel if needed.
Happy New Year!
And thanks for all the help you have provided over the years. 
