To have a window be always on the edge of the screen, anchor it (check documentation for UIRect).
Swipe gesture can either be detected using a dedicated tool for that such as Finger Gestures, or by adding some code using NGUI's existing events.
First you will want to set the UICamera.genericEventHandler to your game object that will hold your gesture detection script. This script will receive a copy of all the events.
Then you will need to create this script. Inside, add the OnPress function.
OnPress(true) set some internal variable to 'true' indicating that you've started your drag event (assuming the drag started where you need it to start). Record the touch location if you need it (UICamera.currentTouch.pos). Inside OnPress(false) check the distance between the saved location and the current touch position (UICamera.currentTouch.totalDelta). If the distance was far enough and happened quickly enough, slide in your window by activating a tween.
If you want it to be gradual like the dock menus on iOS/Android, then you will also need to add appropriate logic to OnDrag.