helloEthereum.js

var helloEthereumContract = 'contract testContract {    function go() constant returns (string) {        return "Hello Ethereum!";    }}'
var helloEthereumCompiled = web3.eth.compile.solidity(helloEthereumContract)
var ethereumContract = web3.eth.contract(helloEthereumCompiled.testContract.info.abiDefinition);
var helloEthereum = ethereumContract.new({from:eth.coinbase, data: helloEthereumCompiled.testContract.code, gas: 199352}, function(e, contract){
    console.log("CALLBACK!");
    if(!e) {
      if(!contract.address) {
        console.log("Contract transaction send: TransactionHash: " + contract.transactionHash + " waiting to be mined...");
      } else {
        console.log("Contract mined! Address: " + contract.address);
        console.log(contract);
      }
    } else {
       console.log("error");
       console.log(e);
    }
})

(Once it has been deployed, takes some time, check TX on etherchain.org)

helloEthereum.go()