The students often do other things instead of learning. They sometimes chat on the internet.
I know exactly what you mean. If students have uncontrolled internet access in the classroom, there's a very strong temptation for students, especially teenagers to go onto messenger or YouTube and do anything but study English.
Apart from patrolling the computers and looking over your students' shoulders all the time, there's not really much you can do about this. I think these types of assignment are not interactive or communicative and are best set as homework to avoid wasting valuable classroom time.
For the classroom, I suggest something a little more controllable. Again, these aren't very interactive... computers suck at listening to students!
New English File provides some good CD-ROMs for Elementary, Pre-Intermediate and Intermediate levels.
Eurotalk offer a wide variety of English learning CD-ROMs that are easy to use and well put together.
And if you've got a big budget:
There's always "Rosetta Stone" - very effective!
Eurolog's "Talk to Me" and "Tell Me More" - very effective for pronunciation but not much else.