You should really get a little switch, maybe PoE capable to run a couple APs?
Connect your Comcast/ISP router to the right-most port, and ZD/Apple PC to other switch ports.
Current issue is that your router gave the ZD an IP address from it's DHCP scope (that it will
share with your PC and all wireless clients).
You can look on your Comcast router's DHCP lease table, for the ZD's current IP address...
I recommend, configure your Comcast router to not use all other IPs in the subnet it's assigning,
so you can give your ZD a Static IP, outside the DHCP scope (that it will share with your PC and
all wireless clients), so you can always reach it (from a saved/favorite bookmark URL).
Does this help?
PS. Upgrade after you have your ZD on the network with Internet access. Check the Release Notes
for that release to be sure it supports all your current AP models.