vista home premium 64

hello,
I have a question i was hoping for some clarification on.
I have been using vist64 and loving it for the most except the dam driver signatures thing.
Now Its my understanding that when running most programs they are in 32bit now does this also mean that when i am running a 32bit program in a 64bit OS that I will still be limited by the 32bit OS specifications like for example RAM in 32bit it can only use 3Gb so does this mean when i run a game or movie make or what ever if its a 32bit program i will only be allowed to use 3gb of ram in stead of the 4Gb i have installed and if this is the case how does this effect dual channel set ups like mine where I have 2Gb*2Gb (4 total) installed :confused
If some one could clear this up for me it would be appreciated