Screensavers are per-user settings. If the currently logged-on user does not have sufficient permissions, you can either temporarily elevate the user's privliges, change the users's/OU's screensaver settings, or log in as an administrator and change the screensaver settings as per-machine in regedit.

Adam brought up some good point. I'll just add a few more.
 
You can always build a user profile with the current specifications and add it to the Default User profile. All new created profiles from then on will receive those settings.
 
http://support.microsoft.com/default.aspx?kbid=319974
 

Quote:you can either temporarily elevate the user's privliges 
EPAL would do this. Though is maybe a security risk.
 
http://www.microsoft.com/technet/prodtechnol/windows2000serv/downloads/epal.mspx
 
The best way of course would be GPOs attached to OUs containing User Accounts were you could manipulate default settings.
 
Ping us back if you need more help.

Thanks for your prompt attention...have decided to try regedit approach. What do i need to change? I have found the reg keys for screensavers (HKEY_CURRENT_USER/Control Panel/Screen Saver.stars) in right pane: (default) REG_SZ (value not set)
Should this data value be altered? not to sure about setting password and screensaver time delay etc...some more help would be really appreciated. Cheers for your help so far.
Matt

Cheers for your help guys,
I copied the registry values from the administrator account (where i successfully setup the password protected screensaver) onto the thin client user. I found these in HKEY_CURRENT_USER/Control Panel/desktop then altered the values in the right pane. Just one question though. On the administrator account i have the 3d flying text, this is not present in the user registry. How can i create a registry key so that i can write in the text for the screensaver
?

That regkey is probably created the first time the default text is modified.