Originally, Valkyries and Disir are different, but Fylgjur, Valkyries, Disir and Norns all show resemblence to each other, and according to some theories, 'Disir' was a broad term to cover all those beings. What is the same in them is that all those beings are associated with fate. Valkyries are the ones who, in the battle, would choose the ones condemned to die. Disir can be both benevolent and malicious toward mankind.
The Disir were worshipped in Scandinavia, their sacrafical holiday was called Disablót, the blót (holiday) was held during Winter Nights (another pagan Scandinavian holiday - suprisingly in winter ), or at vernal equinox. The rites of Disablót were most likely performed by a women.
I don't know if these informations are important... The name 'Disir' simply means 'ladies', while 'Valkyrie' literally translates into 'chooser of the slain'. Valkyries bore other names, like Óskmey ('wish girl') - it might refer to Odin's name Óski ('wish fulfiller'), as he receives the slain warriors in Valhalla; other is Óðins meyjar ('Odin's girls'). Valkyries are sometimes accompanied by ravens or swans.