Ashpoint,

Another good reason not to capture/read/write the users password is that
unless your organization has very good firewall systems and Admins that know how to protect it, it is possible for remote users to sniff out these passwords as they will now be in clear text format.
This will possibly allow someone to much more easily penetrate and damage your system.

I assume that if it is important enough that you want someone to password protect their screen saver, then you have data important enough that you don't want outsiders to take.

I would agree with LLigetfa to try to pop up a dialog box asking them to set a password if possible (I have not tried it either)

Possibly search the Internet for some kind of screen saver that can take advantage of the Network password.