lightroom for two computers

Hi there,

I have lightroom on my macbook, and now bought an imac. I'd love to install lightroom on there as well. I read that it's possible to install lightroom on two computers/laptops.. but how do I go about it? I downloaded the test version, and tried to enter the license key I used for my macbook version, but this doesn't work...

Thanks a lot for your help

Cheers