You say "This is the first time installing security software". Is this system new out of the box? If not, I would recommend running a scan with the Power Eraser utility. See if this system is carrying any threats. I have seen cases where a system is infected, and a BSOD occurs when installing an AV product for the first time.
http://www.symantec.com/business/security_response/malware.jsp
System requirements for Symantec Endpoint Protection and Symantec Network Access Control 11.0.7
Windows 7 (All x86 versions including SP1)
http://www.symantec.com/business/support/index?page=content&id=TECH165172
Regards,
Thomas