[Ethereum] How to create an Ethereum address

If I understand your question correctly you want to be able to see who has deposited Eth to your contract address. This is what event logs are for.

(1) Create a contract where there is an event every time there is a transaction. e.g something like:

contract someContract {   

    address public owner;

    // Set the owner of the contract to be the creator of the contract i.e. you
    function someContract() {
        owner = msg.sender;
    } 

    // This is an event 
    event DepositMade(address _from, uint value);
    event WithdrawalMade(address _to, uint value);

    //Catch all function 
    function() {
        // generate an event when someone sends you Eth
        if (msg.value > 0)
            DepositMade(msg.sender, msg.value);
    }

    // Only the owner of the site can withdraw Eth
    modifier admin { if (msg.sender == owner) _ }

    function withdraw(uint amount, address recipient) admin {
        if(recipient.send(amount))
            WithdrawalMade(msg.sender, msg.value);
        else throw;
    }
}

The important bits are defining an event type event DepositMade(address _from, uint value) and generating an event when something happens DepositMade(msg.sender, msg.value);these events are stored in the event log associated with the address of the deployed contract instance.

(2) You retrieve the events on this contract using rpc eth_newFilter or web3.eth.filter e.g something like:

var filter = web3.eth.filter({fromBlock:0, toBlock: 'latest', address: contractAddress, 'topics':['0x' + web3.sha3('DepositMade(hexstring,uint256)')]});
filter.watch(function(error, result) {
   if(!error) console.log(result);
})

BouncyCastle KeccakDigest does seem to work : https://github.com/Nethereum/Nethereum/blob/master/src/Nethereum.Util/Sha3Keccack.cs

public byte[] CalculateHash(byte[] value)
        {
            var digest = new KeccakDigest(256);
            var output = new byte[digest.GetDigestSize()];
            digest.BlockUpdate(value, 0, value.Length);
            digest.DoFinal(output, 0);
            return output;
}

The complete process of generating an address can be understood by the code in https://github.com/Nethereum/Nethereum/blob/master/src/Nethereum.Signer/EthECKey.cs, especially

public string GetPublicAddress()
{
            var initaddr = new Sha3Keccack().CalculateHash(GetPubKeyNoPrefix());
            var addr = new byte[initaddr.Length - 12];
            Array.Copy(initaddr, 12, addr, 0, initaddr.Length - 12);
            return new AddressUtil().ConvertToChecksumAddress(addr.ToHex());
}