Hi,
The enterprise edition of SharePoint has a feature which needs to be activated if you want to open the form in the browser itself. PFB links for ref -
http://blogs.msdn.com/b/dszabo/archive/2007/03/22/configuration-tasks-needs-to-be-done-to-work-with-infopath-forms-services-and-browser-forms.aspx
Hope this helps!