If you’re interested in downloading the beta (betta) fish wallpaper, or any of the other high resolution nature photograph wallpapers that are seen in the Windows 8 Consumer Preview (Build 8250), look no further. They can all be downloaded in a single zip file hosted here: Windows8_8250_Wallpapers.zip
Also, if you miss the good old days, you can still grab all of the wallpapers from the Windows 7 beta build 7100 released years ago in another zip file: Windows7_7100_Wallpapers.zip
For the full blown experience, don’t forget to download the consumer preview and install it (may I suggest you do this on a ‘spare’ computer or a virtual machine)!