Download the trial version of Lightroom 4.4.1 for the Mac and install it. Then, just use the serial number you have to activate the trial version.
Yes. Your Lightroom License is Single user/owner, Multi platform Mac & or PC. Two installations current with one in use at any point in time.
There is no deactivate / activate process so you can uninstall from one and install on another as many times as necessary. You just use the License Key to activate.
Download the latest version of Lightroom 4 from the link below.