I have a List View in which I have defined a custom cell as a user control.
In the custom cell I given user hyperlink, I am showing a WPF dialog when user clicks on
You would need to get the coordinates of the hyperlink and then set the window position as shown here:
http://blog.fossmo.net/post/How-to-set-the-windows-position-in-WPF.aspx
To get the relative/absolute positions of elements have a look here for some tips:
http://ivolo.mit.edu/post/WPF-Mouse-and-Point-Acrobatics.aspx