Go to Setup-> Configuration->Manage CRM system users
On the bottom right corner click, Add CRM User, a dialog box opens and it has 4 fields,
- Server URL
- User Name
- Password
- User ID
After entering the above information. Save the user and then on the Siebel CRM On Demand. Click on the down arrow and then click "Start CRM Setup". Eloqua synchs with CRMOD and creates the necessary synchs and external calls