I was having problems installing Gtk+ and Navtweak on Vista 64... this is what I did: first download Gtk+ and install that. Only then download Navtweak, then it worked with no errors.

Also, I couldnt even install Gtk+ at first on Vista, it kept throwing out incompatibility errors.. so I downloaded the RAR file on my older XP, then copied over the extracted .EXE file via USB stick over to Vista and then it installed.