I am doing a small two tier cake this weekend and I have never done this before. Do I need to use a cake board underneath the top tier?? are dowels necessary to support the weight? any tips on making sure that the top cake will not shift during transport

the SPS system seems to be highly recommended. I am a hobbyist so I have only so far done dowels. But you need support for every 4" of cake height. For me, the cake boards have in the past absorbed moisture and let the dowels press through, so I now cover the boards with glad press and seal.

Edna (tonedna1) has a great youtube tutorial using dowels.

Welcome to CC. This is a great place to get lots of input from many different people with many different ways to do things, which is good, because then you can find the way you like to do it best This is how I stack cakes. I use a nice solid no flex board like a cake drum for your base cake, then if this is a two tiered cake use a regular cake board inbetween the base cake and what will be your top tier. Under that cake board use plastic howel dowels, which can be bought thru wilton at any craft store. Easy to measure and easy to cut with pvc cutters which I buy at Home depot and only use for food product cutting on my dowels. Another note, as you build your tiers and fill the layers and work your way up, make sure to a check the level of your cakes as you go up. I use a little leveler and sit on cakes and check before I go onto the next tier. This way you get nice even tiers, which is very important , which will help in no leaning or slipping of tiers. One more note, when you cut your dowels to stack a cake on top of, cut them just below your icing line., that way your top tier will sit down slightly into your buttercream and help in keeping that cake in place. Cake construction is a serious thing, very important. I have always doweled like this and never had a cake tilt, slip or move . Happy Cake Decorating , hope this help and good luck

here is a tutorial that is in the articles section of cc
http://cakecentral.com/articles/107/building-the-cake-combination-pillar-stacked-construction

You definitely need the cake board and dowels. The weight is supported by the combination of these. You will frost/cover the bottom tier, then you can mark where you top tier will go by pressing the cut to size top tier cake board where the tier will go. The lift that and put your dowels an inch in, using 4 or 5 (one in the center). Then frost/cover the top tier on the board and put it on the cake. If you are nervous, you can build the tiers when you get to the place... HTH