actually if i am correct the 2 256 sticks should run in dual channel if configured correctly and the 512 in single...
Uhh, no.....you can't have 'some ram' running dual channel while the other stick doesn't.....
With that setup, it will simply NOT run dual channel.
If you had 3 really similar sticks you could run 2x256 in channel A, and 512mb in channel B and in some cases you MIGHT get lucky assuming your board isn't picky and that'll give you dual channel...but considering his mixing brands and speeds I doubt that'll happen.
Beyond that theres no such thing as 'the 256 will run in DC, while the 512mb runs in single'