You can set the default values in the Web Access by modifying the URL. One can use the following URL:
http://<servername>:Port/<path>/WorkItemEdit.aspx?pname=<Name of the Project>&wit=Bug&[Title]=<Title>&[Area Path]=<Existing Area path>&[Iteration Path]=<existing iteration path>
Area path should: <ProjectName>\Area Lvl0\Lvl1 ....
Similarly Iteration Path should be: Iteration\Iteration 0
Hope this helps.
Cheers,Aman Garg