Please take your seats class :)
If you have downloaded movies then you need to convert the files (usually .avi) into the Apple format i.e. .mp4.
If you have dvds then some distributers will encoded the dvd to stop you 'ripping' them. For these dvds there is an extra step.
Google 'AnyDVD'. This software will strip out most encoding protections and copy the DVD contents onto a folder on your PC.
Google 'DVD Catalyst 3'. This softeware will take your downloaded movie/DVD/DVD folder and convert it to the Apple format plus others.
You just tell the software what gadget you have eg iPad, Ipod, Blackberry, Nokia etc and it will sort out file type and resolution.
After the convertion is finished you will have a .mp4 file which is ready to be loaded into iTunes.
Please note - Not all DVDs are encoded. I suggest you try to convert the DVD first and if DVD Catalyst complains THEN you put the DVD thru AnyDVD.
Open up iTunes. Click Edit > Preferences > Advanced. Tick box that starts 'Copy files to iTunes Media Folder. Then OK.
Click File and then either Add file to library or Add folder to libary. I suggest that you set up a folder called iPad Videos for example. Convert all your movies into this folder and then do the Add folder. Saves you adding a file at a time.
And that is it.
Just a couple of things. AiPad movie is typically about 1.2GB. Depending on your iPad model and your movie collection, you may want to tick only the movies you want to sync with your iPad now and just swap the movies in and out of your iPad
For those with iPhones or Touch the iPad file will play on those gadgets. But if you only have an iPhone then telling DVD Catalyst this will get you a file that is about a quarter the size of an iPad file.
Also, your video has now been copied into the iTunes folder so the original file that you ripped the DVD into can be deleted.