Dual channel question

Got a quick question about dual channel config on a Soltek SL-75FRN2 board.
Currently running a Barton 2500 with 1 stick PC2700 512Mb Samsung DDR. I've
got 2 x 256Mb sticks of matched PC3200 Samsung DDR that I'm going to put in
the primary dual channel slot and one of the secondaries. I know this will
enable dual channel; my other system has 2 x 512Mb set up this way. What
happens if I put the remaining original 512Mb PC2700 stick in the last
remaining slot. Does dual channel still function? Will it even boot? And if
you must have matched RAM in all three, does dual channel still operate with
all three slots filled? The m/b manual is none too clear on this. I'd
appreciate an answer to all three of these questions if someone
knows....thanks.