After a quick look I'd just say that for SHELL commands it's better to start and end with single quotes - this leaves the double quotes for long directory names.
Also, why use a shell to make a directory?
Kix can do that just fine... 
IF EXIST ("C:\PROGRA~1\Norton~1")=0 MD "C:\PROGRA~1\Norton Antivirus" ENDIF
[not tested - good luck!]
Ramon
