How to sign a transaction with multiple inputs?
I found the way to do it, so, if anyone is interested, here is how to do it:

When you have more than 1 input, you don't have to remove the inputs that you are not going to sign, you have to remove only their scripts. So, if you want to sign the transaction posted in the question, the first hash would be calculated like so:

'version': 1,
'inputs': (2)
    {
    'output_tx_hash': 'aaaa',
    'output_position': 0,
    'script': the original script, like: '76a914' + hash + '88ac',
    'sequence': ffffffff,
    }, {
    'output_tx_hash': 'bbbb',
    'output_position': 1,
    'script': '', # Nothing
    'sequence': ffffffff,
    }
'outputs': (1)
    'value' : 100000
    'script' : '76a914' + hash of btc pub key + '88ac'
'locktime': 0


And the second hash:

'version': 1,
'inputs': (2)
    {
    'output_tx_hash': 'aaaa',
    'output_position': 0,
    'script': '', # Nothing
    'sequence': ffffffff,
    }, {
    'output_tx_hash': 'bbbb',
    'output_position': 1,
    'script': the original script, like: '76a914' + hash + '88ac',
    'sequence': ffffffff,
    }
'outputs': (1)
    'value' : 100000
    'script' : '76a914' + hash of btc pub key + '88ac'
'locktime': 0


Hope it helps anyone.