Can we mashup two different databases...like SQLServer and Siebel ? I mean is it dependent on a particular technology?

Presto can access all types of standardized data sources: JDBC-compliant databases, REST/SOAP services,  RSS/ATOM feeds, spreadsheets, and even HTML pages.  That's every kind of ERP/SCM/SFA app you can imagine. We have some great demos on www.jackbe.tv that include systems like Seibel and SalesForce.com.