Hi Charmaine,
Strangely enough I had just read an interesting article about Dartmoor Prison in the September issue of Family History Monthly. some good pictures too.
For further information they suggest the following,
Ron Joy, 'Dartmoor Prison, A Complete Illustrated History' (Halsgrove, 2002)
James Trevor, 'A Glimpse of Dartmoor Prison' (Peninsular Press Lts, 1995)
Justin Atholl, 'A Prisoner on the Moor, The Story of Dartmoor' (John Long Ltd 1953)
H.U. Tristan, 'Men in cages' (The Book Club, London 1938)
A.J. Rhodes, 'Dartmoor Prison 1806-1932' (John Lane 1932)
I would think a search on Amazon might be worth doing.
Also, a few files, mainly on policy, are with the National Archives at Kew, in the HO & PCOM series. Other records are with the Devon Record Office, which is closed to the public until January 2005.
They say that there is an excellent small museum dedicated to the prison in Princetown with numerous displays about the prisoners and the lives they led. Tel (01822 892130)
Hope this helps,
jane