Power Users can:
Run legacy applications, in addition to Windows 2000 or Windows XP
Professional certified applications.
Install programs that do not modify operating system files or install system
services.
Customize systemwide resources including printers, date, time, power
options, and other Control Panel resources.
Create and manage local user accounts and groups.
Stop and start system services which are not started by default.
Power Users do not have permission to add themselves to the Administrators
group.
Power Users do not have access to the data of other users on an NTFS volume,
unless those users grant them permission.
Remove the users from the Power Users group, but this will likely break
legacy applications.
You need to test it to see what the ramifications are for your users.
T0 get around it you can try using Software Restriction policies
How To Use Software Restriction Policies in Windows Server 2003
http://support.microsoft.com/default.aspx?scid=kb;en-us;324036
Regards
Mark Dormer