Session: Making Salesforce Analytics Commingle with External Data

The completed URL: https://na14.salesforce.com/00Od0000003CzPQ?pv0=Large&pv1=Express+Logistics+and+Transport&pv2=Web%20Portal&pv3=Total%20Records

The Custom Link with Merge fields: https://na14.salesforce.com/00Od0000003CzPQ?pv0={!Account.Client_Size__c}&pv1={!Account.Name}&pv2=Web%20Portal&pv3=Total%20Records

Alternatively you could leave off "NA .salesforce.com" and just do /*ReportID*?pv0=... 

Here's a good blog post on the subject: http://sfdc.arrowpointe.com/2005/06/09/auto-create-reports-from-web-links/