I have found a great way to use excel for user defined functions

http://blog.mclaughlinsoftware.com/2010/05/28/udf-replaces-vlookup/

I have found a great site that tells how to make a grade lookup in excel without using arrays.

It uses virtual lookups:

'Define a single dimension array of a UDT (record)  

Dim VirtualLookup(1 To 15) As VirtualLookup    

' Record initialization  

VirtualLookup(1).lowerLimit = 0.93  

VirtualLookup(1).upperLimit = 1#  

VirtualLookup(1).letterGrade = "A"

Then you can get and use the values in the lookups like you would with a vlookup in excel.

In a for loop you do this to make the grade = to the vlookup

grade = VirtualLookup(i).letterGrade

I have also been learning how to make arrays in vba in excel

http://www.anthony-vba.kefra.com/vba/vbabasic3.htm#Declaring_Array_With_Dim_Statement