When I start using Ubuntu Linux, some years ago I have no problem on it. Firstly, I use Ubuntu 9.04 Jaunty jackalope on my eMachines. Then, I update on Ubuntu 10.04 Lucid Lynx and the problem was appeared. Every minutes, my display getting flicker and it really annoyed me. After trying some methods, I get this problem goes away. My eMachines is D275, and it might works for other eMachines types or maybe for other laptops which has screen flickering.
To solve that problem, just open your apt.conf, the code is listed here,
sudo nano /etc/apt/apt.conf
Find this or similar on your grub.cfg (use: sudo nano /boot/grub/grub.cfg)