Tried installing the new google maps Latitude on my HTC Touch HD (on Orange UK) from http://www.google.com/latitude earlier today and it didn't work. The cab file downloaded but it refused to install. Several hours later I have successfully installed it or rather upgraded google maps via http://m.google.com > click maps > install now > open the cab file once downloaded. The installer removed your current install of Google maps and installs the new version.
I have not established if there was an issue with the installer that Google fixed or if it was where I downloaded the file from that made the difference but it worked.