I'd like to download the 5th version of Photoshop.

if you mean ps c5, that's available on prodesigntools.com - Download Adobe CS5 Free Trials - All Direct Links without Akamai | ProDesignTools

follow the directions (esp, step 1)

save the install file. it won't remain online.

thank jim @ prodesigntools.com

if you actually mean photoshop v5 from 20+ years ago, good luck finding it and getting it to install.