This is a How To note- A customer requested information on forcing ActiveSync to connect in a quiet mode and default to "Guest Partnership" so that users would not be prompted on the local PC for input.
There are a number of undocumented registry keys for ActiveSync. To implement this you will need to add a key to the registry on the host PC. The following web site has a quick tool that does this too- http://www.pocketpcfaq.com/applications/undocumentedactivesync.htm
I created the attached zip archive with two files and used them successfully with ActiveSync 4.1.0 to set and "unset" the guest-only mode for on a Windows XP host PC.