A simple question that can get complicated but I will try and be brief.If you have the disc.In short you can if you have the installation disc. However, even installing Photoshop from computer A and installing it onto computer B can be, though usually isn't, tricky. All adobe products use a serial number/license key - this key is verified by Adobe's servers to make sure your copy is legal. When uninstalling from any computer you will be prompted if you want the key to stay associated with this computer (computer A in this case) for purposes of reinstalling (back onto computer A), or if you would like to free up the key so you can install the program on another computer (Computer B).If you do not have the disc.Usually, no. There are ways to transfer programs or even entire operating systems from computer to computer but these are a bit advanced for most users. The most common way is a method called 'ghosting'. Put simply ghosting is making a mirror-image file of your hard drive (the file is huge, I have seen between 4 and 70 gig files) and installing that mirror image onto another system.As for your friend's copy of Photoshop it is likely that she has an OEM or Corporate edition. These editions do not sync up with Adobe's validation servers so technically they can be installed, with the same key, on multiple systems. Adobe frowns upon this but these are still quite common (most businesses and colleges do this). Also some OEM releases (I use this term broadly) for the watered down versions of Photoshop, such as Photoshop Elements, originally came with scanners and printers and will rarely not need a key at all.To answer your question better it depends a lot on which version of Photoshop you are asking about. Unless it is an old version (5 years or more) the key will likely be important.Last note: If this is Photoshop CS3 then you may want to look up Adobe CS3 CleanScript for any reinstalling you may need to do. This is a bug-fix by Adobe to correct a problem with reinstalling Adobe CS3 products onto a system.
)