Flower Choices

I just wanted to get some opinions on my flower choices. My wedding is March of 2006 and my colors are going to be purple and pink. (dark to light shades).
I plan on using roses and daises in the bouquets and using tulips in vases. I really don`t know the dos and don`ts on mixing different flowers. I know its my wedding and I can do what I want but I really want it to look nice.
Thanks