Okay..... turn off Windows Defender, or at least the 'active time' components... there isn't any need for them, and I have yet to have Windows Defender save my butt in 3 years using Vista/5 for XP from an infection on my computers.
NOD32 is okay. Spyware Blaster.... never heard of it....wait a minute........ it's okay, but really unnecessary to be running all the time.
Since moving to Vista....... I have yet to see any malware on my PC. None, as far as Norton, McAfee and Microsoft can tell me. So I think Spyware Blaster, like Lavasoft and Spybot are useless to the normal user.
Yes, you should get a firewall IMMEDIATELY. In fact, why weren't you running one before now? That's the first thing I install on any of my computers, is a firewall software even before I go on the internet the first time.