I'm not sure if I got that right, but here
  ,latitude  varchar(20)  '/boe_vr_init/mail_address/geo_co'
  ,longitude  varchar(20)  '/boe_vr_init/mail_address/geo_co'
you're actually selecting the XML node geo_co instead of the latitude and longitude?

So, setting the correct XPath to
  /boe_vr_init/mail_address/geo_co/latitude
  /boe_vr_init/mail_address/geo_co/longitude
respectively might help.

On the other hand, I don't know * about SQL Server so, this post may be a troll. Anyway, just thinking...

Update: Oops, my bad. Forget this post.