Greg Palmer's link is the best site for unattended questions, as is the Forum attached to the FAQ. As to your specific question:
[UserData]
ProductKey=xxxxx-xxxxx-xxxxx-xxxxx-xxxxx
This option is where you enter your cd-key for Setup to use.
In the same section you can add:
FullName="Insert Name"
This option is where you can specify your own name, this is displayed under "Registered to:" in Windows XP's System Properties.
OrgName="Insert Organisation Name"
This option is where you can specify your organisation name, this is also displayed under "Registered to:" in Windows XP's System Properties.
ComputerName=Insert Name
This option is where you can specify a name for your Computer, which is used system and network-wide. This is displayed in the Computer Name tab in Windows XP's System Properties.