If all you want is the 30 day free trial, you can download Lightroom 3.6 from Product updates
After 30 days, you'd need to buy a license, and I'm not sure where you can get one for Lightroom 3. You can try on-line places like Amazon and B&H, but its so old I don't know if they still sell it. And newer versions of Lightroom will not run on Windows XP.
I'm afraid you'll have to go back to Lightroom 3. That is really an outdated version. It runs using the old process version, and you probably won't get the results you are expecting from your raw images. Things have really improved since then. But here is the link to the trial version:
You won't be able to purchase it from Adobe, and it will probably be extremely difficult to find it available elsewhere. If you are using a relatively new digital camera then LR 3 probably will not support the raw format for it. That you can try using the DNG converter and see if it will work with your operating system.
Thanks! I'm checking the matter now, and maybe I can use Lightroom 3.6!!
I've just joined the forum, but I'll learn with time how to use it
On Mon, May 11, 2015 at 11:12 PM, Joshua Cohen <firstname.lastname@example.org>
Thanks! This was very helpful!