most 1.5 templates work fine with 2.x as well. But, if you don’t want bug and security fixes, you can find old versions at http://static.wordpress.org/archives
If you must use older versions:
http://static.wordpress.org/archive/
But you are strongly recommended to use the latest version for security reasons. I’d suggest looking for a different template, or adapting the one you have
Im confused on how to install this template with any version of WordPress…
http://www.templatemonster.com/download/wp_themes/yj2BlOmzK95Ts3tTYV8f/tropical_grunge.zip
It has different files inside….. someone help?
Put the Tropical_Grunge folder into your wp-content/themes folder. So it will look like wp-content/themes/Tropical_Grunge/