It's not just a matter of having computers in the classroom. Students should be able to practice authentic language, and if you don't have such materials that can be used on a computer, then even a computer in class is of no use.

1) ESL teachers should be able to author multi-media featured and interactive lesson material with free authoring software like Hot Potatoes:

http://hotpot.uvic.ca/

2) ESL Teachers should also know how to generate sound files that can be included in the lesson, some free software with voice engines of good quality can be found here:

http://www.cross-plus-a.com/de/balabolka.htm

On that page, download the main program the MS voices Mary, Sam and Mike. You may try the other voices as well but I don't know whether they are free or just trial versions.

3) Note that even if you have loads of material for the computer, it is highly important that students get used to interact in English on a regular basis. A computer or other technology can be no full substitute for this. Here is a download link to a site that offers tons of pre-made activities and entire textbooks for free, and of high quality:

http://www.englishbanana.com

I can also offer you an online one-module course on using technology in the ESL classroom including theory and practical activities to learn more about it. The fee for this is just the equivalent of 50 USD, it includes all study materials, tutoring and a Certificate of Participation. Mail me if you are interested and wish to receive further information.