I tried mapping a network drive to a share on my server, using the UNC path filer.win.sturmnet.orgsturm. Then I hit the “different user name” link – all this looks exactly like it used to under Windows XP. But it works differently: as soon as I log off and on again, the details about the user name and password to use are lost.
The solution was simple: the User Accounts applet in the Control Panel still allows to configure network passwords for an account, but the information I had entered while mapping the network drive wasn’t listed there. I entered it manually and everything works just fine now.