Did a google search on it and found this on Stephen Billington's website (he plays Benteen in the show).
"The new 50-minute docu-film, that Stephen was in, was called 'Custer's Plan' and is one of the episodes in the 'The Wild West' series, that was filmed entirely on the South Dakota [USA] prairie.
Stephen played a Captain, based on a real person that actually fought at the Little Big Horn, named Frederic Benteen. And Stephen gave him a Southern accent!! And if you think that sounds lovely, you're absolutely right!!
General Custer was played by Toby Stephens. Also in the cast, was Roger Clarke as Captain Thomas Weir, Alan Cox as Mark Kellogg, a reporter that rode along with the Cavalry, Nigel Whitmey as Major Marcus Reno, and James Jordan as scout, Mitch Boyer.
'Custer's Plan' was directed by Dave Stewart ('The Human Face' documentary with John Cleese, not from the Eurythmics.) And it is reported to be, the most accurate portrayal of the old Frontier Army in the field, filmed yet - to date.
Evidently it has already aired in UK, and BBC has taken pity on the rest of of who want to see it, because it is posted, in parts, over at YouTube. It is also supposed to air on the Discovery Channel later this year, in the States. You can order one for Zone 2, at the BBC Shop at this URL or at amazon.co.uk, at this URL. But while you wait for your copy to arrive in the mail, you can go over to YouTube and watch it right now! They are all listed under 'Custer', and the URL's are as follows..."
http://www.sbillington.com/LatestInfo.html