The .Net 2 WebBrowser control lets you access the ActiveX control it's
based on via:

wb.ActiveXInstance.

Thus if you add a reference to SHDocVw to your project you can access
the BeforeNavigate2 event like so:

((SHDocVw.WebBrowser)wb.ActiveXInstance).BeforeNavigate2 += new
SHDocVw.DWebBrowserEvents2_BeforeNavigate2EventHandler(ActivityCatalogue_BeforeNavigate2);

I haven't tested a form post on this but it seems to behave just as the
old BeforeNavigate2 does.

Tim