During TFS install, if you recieve error 28100 (Failed to load EventService proxy object: Requested registry access is not allowed.), most probably this is due to regkey left over from a previous TFS installation. TFS uses this regkey to locate registerd servers and make calls against them.
Here is the workaround to solve this problem:
1- open regedit and go to: HKEY_CURRENT_USER\Software\Microsoft\VisualStudio\8.0\TeamFoundation\Servers
2- locate a key under servers with the name: <%YourServerName%>
3- delete this key (not only the value, yet the entire key).
I hope this helps.