There have been many occassions where I've needed to check for a given value within an array in VBScript. There's no built-in function for this, so I crafted my own.

Function IsInArray(strIn, arrCheck)
    'IsInArray: Checks for a value inside an array
    'Author: Justin Doles - www.DigitalDeviation.com
    Dim bFlag bFlag = False
    If IsArray(arrCheck) AND Not IsNull(strIn) Then
        Dim i
        For i = 0 to UBound(arrCheck)
            If LCase(arrcheck(i)) = LCase(strIn) Then
                bFlag = True
            End If
        Next
    End If
    IsInArray = bFlag
End Function

Usage:
If IsInArray(value, array) Then
    WScript.Echo "Yes"
End If