what do i need to implementation ESS on SAP R/3 4.70 ?
IF you are implementing in 4.7, then it is using ITS.
Before starting the Implementation check for the Business Package Installed in the system.
Go to sm30 and display T777WW_SRV
this will have all the ESS scenario with its respective service.
Get it touch with the portal guys and Basis guys and design your home page frame work by going to T77WWW_CTP
Check all the services that you want has its respective service published in the ITS Server.
Of course you have to do some configuration which is at the service level. (If the HR is already in Place)
For custom service, create infotype and programs, easyweb transaction and internet service and publish.
All the best