Do you know what the approximate difference in performance would be in 1 Gig of Dual Channel RAM vs. 2 Gigs of Single Channel RAM?
Well it's about as it reads AFAIK. Dual channel double the ability to input data from RAM to CPU - what your CPU can do with it, is a different story. So, dual channel does improve performance in memory- and processor-intensive stuff - in terms of memory bandwidth, performance doubles, but in reality, the performance difference versus single and dual channel would depend of the type of the application. And, of course, if the processor can't keep up with the increased bandwidth, the processor will become the bottleneck of the system.
Increased memory with reduced bandwidth would only result in improved performance in very memory-intensive programs - mainly image and video editing, when the need for paging data to HD is reduced (which slows things up much more than using single channel mode), but the actual operations would be somewhat slower according to my understanding, before the memory use grows beyond what the RAM can hold.
That said, if I would not be forced to use Vista, I would take the dual-channel 1GB, for now, in stead of single channel 2GB memory. In most cases anyway.