Hi Matt-
The screen resolution is a user-specific setting, and is stored in the
user's profile (located in Documents and Settings).
Although there is not a group policy setting which would allow you to set a
specific setting for the screen resolution for users (this could be an
accidental disaster if set to one the hardware doesn't support), it is
possible to prevent users from altering a predefined screen resolution via
group policy.
In a group policy which linked to a container the user objects reside in,
and where the users have permissions to that group policy, edit the policy
and go to:
User Configuration->Administrative Templates->Control Panel->Display.
You can remove the Display CPL from appearing entirely, or simply remove the
Settings folder tab from being visible for those users.
Please repost if we can help further.