The fact that you only have one computer in your classroom does not mean you cannot successfully integrate technology in your lessons. If you only have a teacher computer, consider adding a TV out card which will turn it into an effective presentation tool that is always available in your classroom. Many classrooms are now equipped with televisions. With a graphics card that has a TV out connection, you can connect your computer to the TV and use it to show PowerPoint presentations, streaming videos, animations, and more.
This content can be used to supplement your lectures and add some variety to your lessons. It can also be used to bring in content that can target different learning styles. A student who is a visual learner may benefit from watching a video of a speech in a history class, or from watching a Flash animation of frog dissection in biology class. You can also use the TV to show student work at the conclusion of your technology lessons. Students will be excited to show off their work to their peers, and knowing that they will have to present their work can encourage some students to put in more effort.
If you have access to at least one student computer, you can use it as a technology center where students can do internet research or work on group writing assignments. To ensure that all students have equal access, you should split up your class into groups of 4-5 students and create a rotation schedule for the use of the one computer in your classroom. You can encourage collaboration within these groups by assigning specific roles to each student in the group (such as Reporter, Data Entry, Editor, etc.).