October 6th 2008. http://www.amazon.co.uk/Battlestar-Galactica-Edward-James-Olmos/dp/B001CD9K9G
Never, there is no fifth season of Battlestar Galactica. It concluded at the end of the fourth season.
Battlestar Galactica - 1978 is rated/received certificates of: Australia:M (DVD rating) Canada:G (Quebec) (VHS/DVD rating) Canada:PG (TV rating) Singapore:PG
Battlestar Galactica The Face of the Enemy - 2008 1-10 was released on: USA: 12 January 2009 Japan: 23 July 2010 (DVD premiere)
Battlestar Galactica season four, part one is available to by on either the 4th or 5th of jJanuary 2009, but is avalible for pre-order now. As for part two, Rumers say it airs on the Sci-fi channel on the 16th of Jan '09 so it should be realeased about a month or two after the last episode.
Battlestar Galactica Razor Flashbacks - 2007 Escape 1-7 was released on: USA: 16 November 2007 Japan: 25 September 2009 (DVD premiere)
Battlestar Galactica Razor Flashbacks - 2007 The Hangar 1-2 was released on: USA: 12 October 2007 Japan: 25 September 2009 (DVD premiere)
Battlestar Galactica is a popular science fiction television show making the DVD's fairly easy to locate at any big box store such as Walmart. You may also purchase the DVD's online at sites like NBC Universal Store, Amazon, and Ebay.
Battlestar Galactica Razor Flashbacks - 2007 Operation Raptor Talon 1-3 was released on: USA: 19 October 2007 Japan: 25 September 2009 (DVD premiere)
DVDs of the first season of the TV show Battlestar Galactica can be purchased from online retailers that offer DVDs, such as Play. They can also be purchased from online mega-retailers such as eBay or Amazon.
I don't think it matters. I watched it after I saw season 3 on TV. Since it was released between season 3 and the upcoming season 4 I'd go ahead and watch it after season 3 since that was when it aired.
Battlestar Galactica Razor - 2007 TV is rated/received certificates of: Australia:MA Canada:14+ (TV rating) Netherlands:12 New Zealand:R13 Singapore:NC-16 South Korea:15 UK:15 (DVD rating)
Battlestar Galactica - 2003 is rated/received certificates of: Australia:M Canada:14A (DVD/video rating) Germany:12 Iceland:L Netherlands:12 Singapore:NC-16 Sweden:11 UK:12 USA:TV-14 (part 1) USA:TV-PG (part 2)