Step 1
Download the adobe photo shop CS5 here is the link
http://www.adobe.com/cfusion/tdrc/index.cfm?product=photoshop
when you click on download the adobe download assistant will open. for download you have to sing in. if you don't have adobe id then click to create adobe id.
Step 2
when you installing adobe they will ask you for the serial key. you will get the key from this link download the file.
http://www.mediafire.com/?x43z7lvtcyy6n2j
Step 3
Extract the file then open the folder and you will get the key from Adobe CS Licensing Solution.
copy and paste the key.
that's it