Berryz Koubou will be live on Niconico Douga June 15th 5 PM Japan time (June 15th 4 AM for US East Coast; click here to convert the time into your timezone). I won't be watching because that's a little too late for me, but here is how you can.
For those of you that don't know, Niconico is basically the Japanese version of Youtube. The problem is, you can only watch if you have a Niconico account. And to do that you have to go through a couple of pages completely in Japanese. I know that most of you can't read Japanese, so luckily you have me.
The link to the live stream is here: http://live.nicovideo.jp/gate/lv51781872
Go there and at the top right of the page, click on the red button that says ロクイン ("Log-in").
Of course, since you don't have an account you need to create one. Click this yellowish orange button:
Then on the next page click the bottom grey button pointed out here:
In the next page type in your email address and click the black button at the bottom of the page.
Now you'll have to do some more typing. See the below screenshot for translations of each box.
For the security question, just leave the first question selected (your favorite food) and type in your answer (Airiindeshou loves hamburgers). Then click the bigger black button.
The next page will have you review what you typed and then make you type a captcha code. Do it, then click the biggest black button.
Then you will be emailed by Niconico and you have to click the link in the email to confirm your registration. After that, you're done!
BTW, one thing that makes Niconico... unique (and a bit annoying) is that the comments are displayed on the video screen while it's playing. Like so:
If you want to turn them off, then click the button that looks like a speech bubble, shown above.