I have seen problems with the CDE screen lock and
xscreensaver, the screen saver won't unlock even when the correct password is supplied or else locks before you can even enter the password, (something to do with third party pam modules and possibly even unreliable DNS!) the only one that has provenm reliable is
xlock but it does not have a timed start-up only manual invocation. I am talking about Solaris 10 on SPARC but looks like you are seeing the same. I believe the Gnome desktop can be configured to run a screensaver on the login screen but would not using
power saving be better (and greener ;-) ?