well i have two zunes in my household. and we have the zune programmed on two different computers. each zune can be used on either computer, when connected as a "Guest" device.
im not sure if One zune software disk can be installed on two computers however, i have not tried it so i cant tell you. but if you have zune installed on two computers, then yes, you can transfer content from both computers to the one zune.
personally, i like to manually manage ALL of my content to and from the zune, so what i did, is under device settings in the zune program, i clicked on "forget device" so the computer does not try to erase and add all kinds of content that i dont want on my device etc. so i always connect my zune as a guest on my main computer for that purpose. this might be useful to you if you plan to simultaneously use two computers for one zune. otherwise i think you'll run into problems with content being erased etc.
but like i said, i dont know if you can use one zune cd to install it twice on two computers. i guess you'll have to try it out and see what happens.
good luck!