Normally if you have the ethernet cable plugged in you'll get the driver 90% of the time and be ready to connect at boot, wireless is installed only about 60% of the time.
This is why it says in the Clean Reinstall - Factory OEM Windows 7
tutorial to put your wireless or ethernet driver in your backup so that if the installer doesn't provide it you can install it to get online quickly to do all Important and Optional updates which will require several rounds with restarts.
. Driver Install - Device Manager Automatically deliver drivers via Windows Update (Step 3)
As it also says in the tutorial you find the wireless or ethernet driver on the PC or device maker's Support Downloads webpage for your model PC or device.
There are tips on installing all of your needed apps and programs and even a mass installer for the most important ones in the tutorial as well.
The Dell Reinstallation DVD self activates.