Now you can work on your Siebel Data without leaving Outlook - from the Siebel user week last month...

...... extending Siebel 7.7 functionality to the Microsoft Office System, allowing Siebel customers to seamlessly leverage the capabilities of Microsoft Office Outlook® and providing transparent access to customer relationship management (CRM) data to users of Microsoft Outlook. Siebel 7.7 supports native use of the Outlook calendar within Siebel .........  http://www.siebel.com/about/news_events/press_releases/2004/040421_microsoft.shtm 

This is a huge win for showing the power of SC and will go a long way in prving the feasibility of this technical integration
Also check out the wiki for .net interop - http://www.pinvoke.net/ . awesome if you you want indepth pincoke questions answered.