moving the downloads folder inside another folder (10.8.2)
The shell in Terminal doesn't like white space in file names. That's what resulted in the error message. You need to use quotes to tell the shell that the second path is a single parameter, try

sudo mv ~/Downloads ~/synktorium/"disktop zi5"/


Alternatively, you could escape the single space before zi5

sudo mv ~/Downloads ~/synktorium/disktop\ zi5/


This is what OS X and Finder would do if you dragged the folder into terminal but it's less clear to someone than using " to prevent mv from seeing three arguments instead of two (a source and destination).