powershell -Or operator not working

Try

If ($User -match "administrator" -or $User -match "kahuna")

Your -or operator doesn't tie the values of the previous operator together. You need to specify a 2nd conditional operator after -or I believe.

Nick is right, vote up his answer. You can also use parens if that is easier to see:

 If (($User -match "administrator") -or ($User -match "kahuna"))

The parens are implied and PSH sees them there anyway. With or without the parens, $User = "administrator" would first resolve to:

If (($true) -or ($false))

which resolves to $true.