Actually, I think you can control the address that you send from if you use "bitcoind.exe" with the command "sendfrom". https://en.bitcoin.it/wiki/Original_Bitcoin_client/API_calls_list
You cannot, sendfrom simply indicates which account's balance to deduct the amount from. It has nothing to do with which coins are selected.
Also, bitcoin technically does not have a "from address". Assuming it was a standard transaction, you can look up which address the input coins were last sent to, but there may be multiple input coins, and each can have one address, multiple addresses (eg. in contracts) or no address at all. These do require non-standard transactions though.
