Nested Transactions

I am writing a program using VC++ 6.0 and SQL 2000 and I am trying to use nested transactions. I have 1 outer transaction and the 2 inner transactions are in sepetrate function calls inside the outer transaction. I have something like this:

BEGIN TRANSACTION;

if (!functioncall1()) // commit if function suceeds, otherwise rollback
{
Rollback Transaction;
return;
}

if (!functioncall2()) // commit if function suceeds, otherwise rollback
{
Rollback Transaction;
return;
}

COMMIT TRANSACTION ;

Both functions contain a complete transaction inside the function call. If either function fails however, I want to do a rollback of the entire transaction. This is not happening though. If functioncall1 suceeds and the transaction in that function commits, then if I do a rollback during functioncall2, the transaction in functioncall1 is not rolled back. This seems to be directly opposite of the SQL help for transaction. Am I missing something obvious here?