11/29/12: I've tried out the new Keyhole TV update. You have to create a password to open it and click on a few things to get the channel list to come up, but it does work. If you've used it before, make sure you have the newest version. If you're downloading it for the first time, give yourself enough time to figure out how it works and to work out any issues. The channel list seems more erratic than in the past. Readers reported not being able to watch the Yokohama International Women's Marathon and only a few seemed able to get the right channel to watch the International Chiba Ekiden. The Fukuoka International Marathon will be will be broadcast Dec. 2 on TV Asahi starting at 12:00 p.m. Japan time, with the race starting at 12:10. Scroll through the channels with the largest numbers of viewers first to find whether TV Asahi is available.
The best option for watching Japanese races online from overseas is a free P2P program called Keyhole TV . The quality and reliability of the streaming varies, but it is usually at least watchable.
Go here or here to get the Keyhole TV player. If you have downloaded Keyhole before, make sure you have the most recent version of the player for optimal performance. This site sometimes has some channels not available on Keyhole. JRN also offers live English race commentary for some races via Twitter @JRNLive.
To use Keyhole, once you have downloaded, installed and opened the player a list of available channels will appear in the main window. When you single-click a channel the name should appear in English if the channel name is in kanji. Scroll through the list until you find the right channel, then double click it. The channel should open immediately. To watch NHK, entering the name of the network as a password will usually get you in. If the streaming freezes, stopping the video and then re-opening the channel will usually bring it back. It's probably worth it to download the player and try it out well before the race broadcast begins to make sure you don't have any trouble.
JRN recommends timeanddate.com's World Clock Time Zone Converter for figuring out broadcast times in your area.
Please note that Japan Running News is not affiliated with Keyhole TV and makes no guarantees about its quality, reliability, safety or the availability of any particular race broadcast. That said, we regularly use it ourselves when travelling internationally and have never had problems with it.