I eventually figured out my own problem. Hopefully this will help you with
your issue, Nyls.
There is a link on the sidebar of the ease of access center that directs you
to change administrative settings. From there, you can have the option of
determining which utilities get started on the logon window. This has seemed
to work for me, although it appears that the onscreen keyboard is given a
lower priority in the startup order on my system and doesn't show up until
about 10 seconds after the logon screen first appears.
Does anyone know how I can boost the priority of the onscreen keyboard, or
any application for that matter, in the system startup list on Vista?