Well when I downloaded it, it was the time I updated to NavCore 7 as an option came up asking me if I wanted to update.
However, I think it should still work even if you download the executable file from TomTom's site.
During the installation of HOME 2.0 there was an option to keep 1.5 which is what I choose. You may want to uninstall 2.0. Then try installing 1.5, and right after install HOME 2.1 (that's the latest version of HOME).
See if that works for you.
HOME 2.1 - http://www.tomtom.com/support/index.php?Language=1&query=home+2.1&FID=7602
I tried the above, but it still over rides 1.5 - even when I go straigt to the program and try top open it. I am using Vista Ultimate and run it in elevated mode.
Did you possibly rename the .exe file to tomtom2 also and set up new shortcut ?