It sounds to me that he has a roaming profile that is not configured to exclude certain folders from being copied with his profile, such as Temporary Internet files and cookies.
As a network administrator I inherited the same problem with a lot of users when I accepted the position and had to configure it using System Policies (NT) or using Policy Editor in the Windows 2000 MMC. After doing this, their login times went from 20 minutes in some cases to 15 seconds.
Thanks for the suggestion. Your intuitions are in fact correct; roaming profiles do often take much longer to boot since the system is searching for any additional networked information about the profile. If the machine is not networked, or the roaming profile resources are not available, booting can take a long time.
This was first published in March 2003