Can someone plz tell me what is the use of the software Microsoft Office SharePoint Server 2007? Is it a webserver like IIS?
not really, although it does publish. It's essentially a corporate portal which allows a central repository for files, version control etc. no real use for the home user. This will get you started: http://www.sharepointsite.com/hosted_sharepoint/understanding_sharepoint/
It helps businesses (not individuals) to collaborate, share, and interact more easily. It has a bunch of advantages though it might become quite expensive if you intend to standardize it throughout your company. Along with MS Office products it is very powerful though. There's a test drive on Microsoft.com which includes Sharepoint services. Go and take a look.