Yahoo messenger?

I want to change the default setting on yahoo messenger to when I log on, the messenger window does not appear on my desk top. Note I do want to be logged in, I just dont want the window to pop open. Can this be done through Regedt32 or a VBS Script. Some one show off for me and help me out.
NOTE: I do want the messenger to log on, and stay on the system tray. Just dont want the dialog box to open up.