>I heard that with SPS (SharePoint Portal Server) can use existing data effectively and capture information the way it makes sense to our business and the search and index facilities help access data easily.
>
>And I know that OLAP is a great tool for Collecting data from several heterogeneous sources, help planning and decision-making, Aggregate and summarize data, Can deliver data to business users faster, ...etc
>
>To make use of our existing data (SQL) effectively, which product you think I should promote?
>
>Is there any comparison article between the two products?

This is not two differnt prodicts.
SQLServer2000 OLAP is used for businness inteligence you can find more info at http://msdn.microsoft.com/library/default.asp?url=/code/list/olapservices.asp

Using OLAP n-Cubes you can drill data and present different usefull statistic.

SharePoint Portal server is used for connecting people in organization which use it. IRM service help officers to share documents helping them to compleate project fast. There a lot of new services added to Office 2003 related to share services.
Look at http://msdn.microsoft.com/library/default.asp?url=/library/en-us/odc_sp2003_ta/html/sharepoint_deployingwebparts.asp

HTH