For security reasons you might want to ensure that your network interface(s) are administratively down when you boot your machine.

This might seem a little out of place, but customers often use FireDaemon to run the following batch file when their machine boots (i.e. prior to login). Then when they log in for the first time their network interface is enabled and brought up. Here's the batch file:

ipconfig /release
net stop "dhcp client"

When you log in, make sure the following is in your Startup folder:

net start "dhcp client"

The other option is to make the DHCP Client service start manually (or on Vista make it demand start).