You can download trial versions at the site linked below and use you current serial number to activate. A problem you are going to run into is having a license for a PC and wanting one for a Mac. For information on that you will do best to visit the second link provided below.
Be sure to follow the steps outlined in the Note: Very Important Instructions section on the download pages at this site.
I've checked your account and see that the serial number given(for LR4)is compatible on both Win and MAC. You can use the same serial number during installation on your MAC. I do have another query for you.
LR4 purchased in March 2012 is an upgrade version. Upon further investigation I found you do not have any prior versions registered on your account.
When you try installing LR4 on your new MAC you may be prompted for the serial number of a prior version(after you enter the serila number for LR4). Please keep it handy.
Thank you for your prompt response. I do have a prior version of Lightroom on the old computer, which is not functioning properly. Do you have a suggestion as to how to retrieve the serial number?
Of further concern is where, and how, to get the Lightroom 4 download. It never installed on the old computer because it was an XP operating system, which is not compatible with LR4.
I hope my brief words accurately portray the need for very specific instructions and guidance. Something that has thus far eluded my inquiries.
Again, thank you.
I've mentioned my answers inline.
I do have a prior version of Lightroom on the old computer, which is not functioning properly. Do you have a suggestion as to how to retrieve the serial number? : Check if this link helps : http://helpx.adobe.com/x-productkb/global/find-serial-number.html
Of further concern is where, and how, to get the Lightroom 4 download : Download the product from here : http://www.adobe.com/downloads/ (select the product and OS from the list and start the download).
Alternatively since you've bought the product follow the instructions on how to download a product from here : http://helpx.adobe.com/creative-suite/kb/find-download-link.html
I’m not at the home office where the new computer and Lightroom are located right now. However, I have been to the Adobe site to download my purchased version and there is no button or link to do so and that is what began all this communication to begin with. Therefore, I will need to know how to accomplish that function when I get back home. Your assistance will be appreciated. Also, if the other computer fails to boot up, which has been a problem, how will I retrieve the older Lightroom serial number?
Download the trial version for Lightroom 4 from here : http://www.adobe.com/downloads/ (select the product and OS from the list and start the download). During installation enter the serial number for LR4 first and then the previous version. In case you are unable to find the old serial number you'r best option would be to contact Adobe Support.