I own many movie videos on my PC. How do I copy some to the Ipad?

If they are in a compatible format then you can add them to your computer's iTunes via File > Add To Library, and they shold go into the Movies part of your library. You can then try syncing them to the iPad's Videos app via the Movies tab on the right-hand side of iTunes, in a similar way to how you use the Music tab to sync music.

Are you able to get them into your computer's iTunes library ? If you can, and they don't all then sync to the iPad's Videos app when you select them on the Movies tab, then you could try selecting them in the Movies part of your library and doing File > Create New Version > Create iPad Version and see if those versions then sync over.

Or there are a number of apps in the app store that say that they support AVI videos - i haven't got any of them so I don't kow how good they are, but searcing for AVI gets a number of results, and they probably use file sharing to get content to them from your computer.