You want to connect this to a Time Capsule? For what purpose? The time capsule already has a built in HD for wireless back ups.
I don't have that version of the Free agent dock. I actually have the one that is powered and comes with an AC adaptor. The powered version has two USB ports in the rear and one USB port on the side.
I have my powered dock connected to my Airport Extreme Base Station. I have a USB printer connected to the dock. I have the 640 gb Seagate HD sitting in the dock. The end result is I now have wireless Time Machine backups and a wireless printer. I highly recommend this setup. I still have two free USB ports on the dock too! I prefer the powered dock to rest assured that my time machine backups won't screw up due to lack of power.