I use a logon script for this in a GPO at domain root level. A simplified version might look something like:
Set ADSysInfo = CreateObject ("ADSystemInfo")
Set currComp = GetObject ("LDAP://" & ADSysInfo.ComputerName)
Set CurrUser = GetObject ("LDAP://" & ADSysInfo.UserName)
if CurrComp.operatingSystem = "Windows 2000 Server" or _
CurrComp.operatingSystem = "Windows Server 2003" then
' send email via whatever SMTP server/etc you have in place
' this will be different depending on the server so i can't give code
' CurrUser.sAMAccountName - user account name
' CurrComp.cn - name of server being logged on to
endif
You'll need to dig out ways of sending email via script on TechNet for the missing part of it