Dales,
ESXi, we cannot install naviagent. ESXi carries NAVIREG code by default, and this option is enabled by default. See the screenshot for same. The job of this navireg is to perform automatic registration of ESX hosts in Navisphere.
FYI...I came across an issue in update1, where automatic registration didn't worked, the same worked very well in Update2.
Thanks,,
Ramesh. Geddam,
VCP 3&4, MCTS(Hyper-V), SNIA SCP.
Please award points, if helpful
http://communities.vmware.com/blogs/rameshgeddam