Wired had a fantastic post on how to stream video to an iPad from a network drive, without a computer:
The innocuously-named FileBrowser is an iPad app which lets you access files on your computer over the local network or the internet.
This is a function shared by roughly one zillion other apps in the store. What makes FileBrowser different is that it can access network-attached storage (NAS), letting you stream video and music to your iPad from a Time Capsule or other network drive without switching on a computer.
Pretty darn sweet if you ask me. Learn how to do it here.