Yes and no.
You need to install a second copy of Carrara And then copy and paste the plugin. The plugin installer only recognizes a single install so you need to juggle things a bit. If you want to keep your current Carrara install at v3 then you need to
1 upgrade to v4
2 copy the v4 plugin to your second Carrara install
3 uninstall the plugin
4 reinstall v3
I really need to post a zip version of the plugin for this scenario...