I have a formula which references a cell which has been defined as a Name
under Insert/Name/Define... The formula works just fine. However I want
the named definition to be variable based on the input of another cell. For
example:

Input cell = A1 = 100

Possible Name Values:
B1 = 1
B2 = 2
B3 = 3
B4 = 4

If A1<=100, then define range name XYZ = B1
If A2 100 and <200, then define range XYZ = B2
If A2 200 and <300, then define range XYZ = B3
If A2 300 and <400, then define range XYZ = B4

Ideas?