To generate a genesis block for a private network in frontier ethereum, all you need to do is execute the following lines of code:
{
"nonce": "0x0000000000000042",
"difficulty": "0x000000100",
"alloc": {
},
"mixhash": "0x0000000000000000000000000000000000000000000000000000000000000000",
"coinbase": "0x0000000000000000000000000000000000000000",
"timestamp": "0x00",
"parentHash": "0x0000000000000000000000000000000000000000000000000000000000000000",
"gasLimit": "0x16388"
}