String manipulation help

I have a string that could contain any of the following:

newString = "joseph OR medal OR gold"
newString = "christopher OR medals"
newString = "medals"
newString = "medal"

I want to check "newString" for "medals" or "medal", then I want to replace
the "OR" with "AND" . . something like this:

If newString has "medals" or "medal" Then
  Replace "OR" with "AND"

So the string "joseph OR medal OR gold"  would be "joseph AND medal AND gold"

Also . . .  If just the one word "medals" or "medal" is in the string (newString = "medals")
I want to  Response.Redirect("default.aspx") . . like this:

If newString has ONLY "medal" or "medals"
  Response.Redirect("default.aspx")

thanks