IF formula with multiple conditions

Sorry, but I'm getting myself confused on an if formula, and hope I can get some help with it.

Here's what I'm trying to do:

1) IF AL2 contains something, put a blank
2) else, if AL2 is blank, and IF AH2 AND AI2 are both blank, put a blank.
3) However, if AL2 doesn't contain anything, and IF AH2 has something, put the results of the first Vlookup
4) IF AH2 has nothing, and If AI2 has something, put the results of the second Vlookup.

Below is my attempt so far, without even attempting the first condition. Any help on this is greatly appreciated.

=IF(AND(Countif(AH2,"",AI2,""),"",IF(CountifAH2,""),VLOOKUP(AH2,'[FY 2011 Contracts in a Department Under Audrey.xls]Formatted for BMT use'!$A:$C,3,FALSE),VLOOKUP(AI2,'[FY 2011 Contracts in a Department Under Audrey.xls]Formatted for BMT use'!$A:$C,3,FALSE))