soo bummed, did not turn out..*croissants*

Of course, I can't tell you what the problem was, as I'm no expert on croissant, and your post was lacking in detail regarding what, exactly, went wrong, but I can tell you the yeast almost certainly wasn't it.  The simple fact is dry yeast (particularly instant/quick rising yeast, which has much finer granules than active dry) will produce an outcome every bit as good as fresh yeast.  In fact, I would go so far as to say, for your average home baker, there is absolutely no reason to use fresh yeast, and certainly valid reasons not to, not the least of which: it goes bad (home bakers don't bake in large volumes, and so won't use the yeast up fast enough), and it's difficult to find.

As for how to treat the yeast, if you're using instant yeast, just throw it in with the dry ingredients (if you're using active dry, you might want to dissolve it in liquid to ensure the granules incorporate into the dough properly... though you don't actually need to proof it, as so many directions suggest).  And the temperature of the milk should make very little difference, so long as the final dough is at the desired temperature (I've made overnight doughs that use ice water, along with instant yeast, and they always turn out great).

I've tried making the croissants in Baking with Julia, substituting dry yeast for the fresh, and they didn't turn out at all.  Now I use a recipe by Beth Hensperger for the dough and the rolling in of the butter, and for the shaping and rising and baking, I go with my own readings of a few other recipes.  I'll post that recipe, if you'd like.