First off, Select-Case only works with one variable. So personally I would use a dictionary of dictionaries:
Option Explicit
Dim dicTerm :Set dicTerm = CreateObject("Scripting.Dictionary")
Dim Amort
Dim Rate
Dim Term
Term=Inputbox("What is the Term length?")
Amort=Inputbox("What is the Amort length?")
Set dicTerm("2") = CreateObject("Scripting.Dictionary")
dicTerm("2")("2") = .88
dicTerm("2")("5") = 1.05
dicTerm("2")("10") = 1.09
dicTerm("2")("15") = 1.10
dicTerm("2")("20") = 1.10
dicTerm("2")("25") = 1.11
Set dicTerm("3") = CreateObject("Scripting.Dictionary")
dicTerm("3")("3") = 1.07
dicTerm("3")("5") = 1.20
dicTerm("3")("10") = 1.26
dicTerm("3")("15") = 1.28
dicTerm("3")("20") = 1.28
dicTerm("3")("25") = 1.29
Rate = dicTerm(Term)(Amort)
msgBox Rate