Is it possible to transfer movies that I have downloaded on my windows PC to my iPad so that I can watch them?

yes...you need to convert them to mp4 format or ipad format with converter such as total video converter or wonder share video converter or xilsoft

Yes but don't have to convert them to mp4. If you install buzzplayer, you can download (or copy through iTunes) and read any video file format with buzz player, inc divx.
The oher great thing with buzz player is that you don't necessary need to have the video file physically present on the iPad: you also can stream the videos from your pc or from a server....
IMO if you intend to use your iPad to watch videos, buzz player is a must-have (and I've tested many video/divx players out there).

If this advice doesn't get you through the sync process of movies I strongly recommend you use the search function on the forum. There are some brilliant threads on here about syncing movies onto your iPad with step by step instructions. All it takes is a little bit of searching. Good luck, and remember, search is your friend.

Proud owner of a 32GB wifi iPad2 iOS5.