I would go with the dual channel anyday. My scores jump considerably when going from dual channel, to single channel.
On my AMD XP setup, going from 1 gig single channel, to 1 gig dual channel, made my RAM scores in PCMark02 jump 500 points. (AMD 2800, PC3200 1 gig)
On my father-in-law's system, I swapped out his motherboard for a dual channel board (Only PC2100, 512 MB, his board didint' support Dual Channel), and his scores jumped 1100 points. (AMD 2200, PC2100 512 MB)
I don't think you are going to notice the difference between 1 gig and 1.2 gig in RAM, especially with what you are using your computer for, however, I think you will notice the dual channel.