Here is how I accomplished the task:
I created a global group (let's call it "globgroupx"

and put all of the users that I wanted to be power users into that group. Then I created a script (actually, I found it on a website

) that places the members of that global group into the power users local group on all of the machines. The script was placed into the startup script for the group policy. Here is the script, where my global group=globgroupx and my domain=domain.com:
poweruser.vbs
***************************************************
On Error Resume Next
set WshShell = CreateObject("WScript.Shell"

set netobj = CreateObject("WScript.Network"

CompName = netobj.ComputerName
UsrDomainString = "domain.com"
LocalGrp1 = "Power Users"
GroupString1 = "globgroupx"
' add a global group to local group
Set GroupObj = GetObject("WinNT://" & CompName & "/" & LocalGrp1)
GroupObj.Add ("WinNT://" & UsrDomainString & "/" & GroupString1)
Set GroupObj = Nothing
*******************************************************
I hope this helps.