how to stop apache2, mysql from starting automatically as computer starts?

MySQL is handled by upstart. In 11.04 you can use the new override feature to modify the starting behaviour:

echo "manual" >> /etc/init/mysql.override

See the section "Disabling a Job from Automatically Starting" in the Upstart Cookbook

Apache still uses traditional SysV init scripts so you use

 update-rc.d -f apache2 remove

to remove the links from /etc/rcX.d or, alternatively, use

 update-rc.d apache2 disable

which "disables" the script by changing it from a start script S91apache2 to a stop script K09apache2. This is reversible by update-rc.d apache2 enable.

Interestingly, it's a different answer for each package in 11.04.

• apache2 uses System V style init scripts. To disable it from boot:
  sudo update-rc.d -f apache2 remove
• However, mysql uses an Upstart job, to disable it, create an "override" file:
  echo "manual" | sudo tee /etc/init/mysql.override

To learn more about override files, see: The Upstart Cookbook

This thread will help you: https://superuser.com/questions/35151/how-do-i-stop-services-from-starting-on-boot-on-ubuntu