I've only stacked cakes once before, and they were quite sturdy cakes, so I just put them on top of each other(3 of them)....now I hear you are supposed to put plates / boards in between and use dowels for support???! 
One little question - do you put the board under the second cake before covering it together with the cake, or do you cover the cakes and put the boards in between?? 
put your booards under your tiers before you ice them... then stack. make sure you have dowels of some type in the lower tier to suppert the uppers. I think there is a how to on this site somehwere....
Here this should help
http://www.cakecentral.com/article23-Teired-Stacked-Cake-Construction.html
Everything you ever wanted to know about making your 1st tiered cake:
(Has illustrated common cake support systems with complete and accurate directions....and so much more.)
http://forum.cakecentral.com/cake-decorating-ftopicp-5958955-.html
Illustrated guide to cutting neat slices of tiered cake by indydebi:
http://tinyurl.com/5gxsqf
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