assuming you have the sysprep folder download and sitting in the c:\. run sysprep.exe there you will able to input all the infor such as computer name, domain, work group ... or you can make your own sysprep.inf like this one: my sugestion is to make your own, much easier.
;SetupMgrTag
[Unattended]
OemSkipEula=Yes
InstallFilesPath=C:\sysprep\i386
[GuiUnattended]
AdminPassword="password"
EncryptedAdminPassword=NO
OEMSkipRegional=1
TimeZone=20
OemSkipWelcome=1
[UserData]
ProductKey=
FullName="Company Name Goes in Here"
OrgName="Company Name Goes in Here"
ComputerName=*
[TapiLocation]
CountryCode=1
Dialing=Tone
AreaCode=630
[SetupMgr]
DistFolder=C:\sysprep\i386
DistShare=windist
[Identification]
JoinDomain=
DomainAdmin=
DomainAdminPassword=
[Networking]
InstallDefaultComponents=Yes
[SysprepCleanup]
[SysprepCleanup]
================================
save it as sysprep.inf once you input all those info.