Linux managing stuffs

How do i set the date and time in Linux? Where do I need to commands that I want to run automagically after startup has finished. In other words… I have three lines that I initiate after I login as root everytime I boot the machine. the commands are like the following:

/sbin/ifup eth0

I want these to run only once per boot-up and only once. So I don’t want to put them into .bashrc as has been suggested to me before. That would make them run everytime I logged into a shell.

Adam