Sometimes people may have issues with the "Hosts" replacement method either because they don't understand where the file goes or how to deal with the permissions and overwriting the original Hosts file. So, here's an alternative method to cracking Adobe Creative Suits 5 Master Collection or any products in the Adobe Creative Suite 5 series.
Just copy the DLL crack file (amtlib.dll) from either the 32 Bit or 64 Bit folder depending on the version of the product you installed into the installation directory, NOT into any other sub-directory. You will be prompted to overwrite the original, click Yes or Copy and Replace. Run Photoshop and enter a serial key.