Decode from SQLPLUS

[rynorem]

I trying to take a SQLPLUS script and put it into Access. Got a mojority of it to work great but am having trouble with decode some vacancy jobs codes to words.
How would you translate this for Access:

decode(a.allowed - nvl(a.assigned,'0'),'-1','EXCESS - 1','-2','EXCESS - 2')).

Allowed is how many they can hire in that department.
Assigned is how many is there now.

THanks, Jamie