One option for watching Japanese races online from overseas is Keyhole TV . The quality and reliability of the streaming varies, but it is usually at least watchable. A paid premium key usually results in significantly better quality. Go here or here to get the Keyhole TV player, or just Google it to find up-to-date sites offering it. If you have downloaded Keyhole before, make sure you have the most recent version of the player for optimal performance.
Another option that looks promising is http://www.jpplayer.com/
This also looks good but takes time to set up so might be a better long-term option: http://www.nihonnamaterebi.com/
A list of these and other options: http://www.d-addicts.com/forums/viewtopic.php?t=73546
This site sometimes has some channels not available elsewhere.
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.
Timeanddate.com's World Clock Time Zone Converter is useful for figuring out broadcast times in your area.
Please note that JRN is not affiliated with any of the above streaming sites or services and takes no responsibility for their use.