Open a web page exclusively

I've a problem with an intranet page: I have to open a page that modifiy an xml file exclusively.
I have to do that because otherwise maybe some update will be lost...

I use c# in asp.net and I'm a really newbie...

there's a way to do that?

I mean with exculsively that : I want to open the page edit.aspx. If Another user (I use the integrated windows authentication) has already opened this page, I want to redirect to another page telling that a user is currently modifying the files...


thanx a lot