How can I get a network connection to load completely before a user can log in?

Solution 1:

You could enable the Always wait for the network at computer startup and logon Group Policy setting.

It lives in Computer Configuration\Administrative Templates\System\Logon.

Alternatively, you could map your network drives with Group Policy Preference items, which should eradicate this problem, and the frustration of waiting for crappy drivers or hardware to properly and fully initialise.