Go to https://ico.beth.jp/participate , select ETH, and it will give you an address to send ETH to. This address will be active for only an hour, so make sure you at least have the transaction started before the end of the hour.

You can always initiate more transactions later if need be, but just keep in mind that the individual addresses "expire". Also, if it takes longer than an hour for the transaction to clear (as mine did with BTC), it will still go through just fine.