If your application will be used with Access 2003, seems to me you should exclude features 2003 doesn't support.
However, if you must have Tempvars, see whether a conditional compiler constant approach would make it work for you.
Option Compare Database
Option Explicit
#Const Aversion = "2007" 'conditional compiler constant '
Public Sub HelloWorld()
Dim strWho As String
strWho = "World"
#If Aversion = "2007" Then
'* your 2007 feature code here *'
strWho = UCase(strWho)
#End If
'Aversion 2003 -> Hello World '
'Aversion 2007 -> Hello WORLD '
Debug.Print "Hello " & strWho
End Sub
Check Access' Help for more information about #Const and #If.
I haven't tested this, but I think it could work. You might need two copies of your database: YourDb2003.mdb; and YourDb2007.mdb. In YourDb2003.mdb use "2003" as the compiler constant, and "2007" in YourDb2007.mdb.