how to transfer videos to ipod touch?

Why not? Are you getting any error messages when you try? Do these videos play okay in iTunes? How do you have your iPod set up to sync movies?

Perhaps these two articles may help.

iTunes: May be unable to transfer videos to iPhone, iPad, or iPod

iTunes: Frequently asked questions about viewing and syncing videos

B-roc

You'll first want to make sure that the video isn't just on your computer but that it's in your iTunes library as well. This can be achieved by dragging and dropping the video into your iTunes, provided the video is in a format that iTunes recognizes. Once it's in your iTunes library, try syncing your iPod again. Make sure that when your iPod is plugged in, you go to the little iPod icon in iTunes and enable the checkbox that says "sync all videos." If that doesn't work, just find the video(s) you want to transfer to your iPod and manually drag them from your iTunes video library onto the iPod icon and it should sync. I hope this helped.

Sounds like the format is not compatible with the smaller screen device.Have you tried using HandBrake converter? It is free and has presets for iPhone/iPod touch and iPad compatibility.