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Yes it is, I have done it on mt 2007 15" MBP. I installed a Samsung 840 evo 250GB SSD.

Check out
http://eshop.macsales.com/installvideos/macbookpro_15/

All I did was connected new SSD via USB formatted to Journalled MAC OS Extended (I had an external HDD case to use) made a clone of my hard drive using ccc (https://bombich.com/), booted via USB to make sure it was done correctly, installed SSD into my MBP.

Only tools you need Philips 00 screwdriver and a Torx T6 screwdriver. Use the video, I used it and it helped heaps.

The SSD makes a HUGE difference to this machine.
 
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