I have a ASP.NET 2.0 web application that should upload a ppt file and then extract its slides to images. For that I have imported office.dll and Microsoft.Office.Interop.Po
When considering using Office Automation on the server, you might want to take a read through the info in the following KB article.
http://support.microsoft.com/kb/257757
A key phrase from the above link
Microsoft does not currently recommend, and does not support, Automation of Microsoft Office applications from any unattended, non-interactive client application or component (including ASP, ASP.NET, DCOM, and NT Services), because Office may exhibit unstable behavior and/or deadlock when Office is run in this environment.
And I can confirm that the above is very true, and not just MS trying to discourage you...