This is how I do it:
- plug iPhone into PC/Mac
- I go to the iPhone under Computers and navigate to the folder where the pic/movs are.
- drag the video from that folder to a folder on my PC.
- go into iTunes
- plug iPad into computer
- once connected, click on the iPad on the left hand side to bring up the iPad details
- go to the photo tab and check the box to sync photos (and make sure you check include videos)
- add the specific folder you moved the video to on your PC to the sync list
- sync your iPad
Once the sync is done, the movie will appear in the relevant folder of the Photos app.