I have been having major problems trying to set up my Slingbox on my Imac, here is my configuration:
1, My internet comes in Via a CDMA usb dongle, it is then shared to the TC via ethernet
2, The TC is set up however the slingbox never gets an IP address and the network light goes on and off.
I have searched everywhere trying to find an answer for this but there are no good guides to this. I have even tried extending my network via an airport express but that does not work either.
Is your Time Capsule setup as a router and is ditributing DHCP IP address? If so, I'd try to perform a factory reset on your Slingbox as described (http://support.slingmedia.com/get/KB-1000038.html). Its possible that the Slingbox has retained the network configuration of an older router.