Windows 7, just as was the case in Windows Vista, has a auto defrag option. Once the system reaches a certain fragmentation point the system will auto defrag. It should never get beyond 30% or so i believe is the threshold. So runnign defrag software weekly/monthly is not necessary.
As for the firewall that one can be argued. I have nto isntalled a firewall for at least 3 years. Not in Vista and not at all in Win7. While the firewall is good, it isnt perfect. But then again what is...
The point is that with the PROPER protection the Windows firewall is more than enough. Meaning you have a decent router with a built in firewall, which is active, your network is secure and so on. With the proper steps it will be hard for even the most savvy hacker to access your system.
AV we have a whole topic stickied for this reason. They are all listed with votes. We have another whole topic about MSE. There is more than enough information provided to make a accurate call on which protection will be right for you.