you can't, obviously. so start up a virtual machine, run a new version of your OS, and install it there. you should also take care to isolate the network connection of your vm as much as possible (and/or monitor it). i'm not promising this is sufficient - good luck :o)

ps to answer your other question - antivirus scanners look for patterns in the file itself, so they don't need to install it, but are vulnerable to alternative packaging, modified code, etc etc (of course, scanners also check for problems with installed files, but the first line of defense is to inspect the data - including unpacking zip files etc).