For a discussion of the different forms of yeast and how they should be used, you might want to take a look at this PMQ Think Tank thread, especially Tom Lehmann's post: http://thinktank.pmq.com/viewtopic.php?p=50947#50947
. I personally freeze my dry yeast, so I don't follow Tom's "use by" advice.
Since, in your case, you are converting in the opposite direction, from IDY to ADY or fresh yeast, you will need to increase the amount of IDY, by weight, by about one-third to get to ADY and by threefold to get to cake (compressed) yeast. In the case of using cake yeast instead of IDY, you will also have to reduce the formula water by the difference in weights between the IDY and cake yeast (to compensate for the water content of cake yeast). In most cases in a home environment, that difference might be too small to worry about.
Sometimes, when I am lazy, I use the yeast conversion table at http://www.theartisan.net/convert_yeast_two.htm
to determine the conversions or to confirm my own conversions that I do in my head or using a calculator.