This is only my Opinion here so take it with a grain of salt.
If you really want a secure computer then download one of the free Linux flavors and learn to run it on your computer. Windows will always be compromised by the ability to be easy to use. Somewhere in making it easy to use Microsoft had to compromise security.I personally have windows computers that have very few updates, and no security software installed. This is because i do not connect these computers to the internet that i can do this. There is only one computer that has the latest updates, runs Avast Anti-virus and uses both a software and a hardware firewall. This is my internet computer.
On partitioning a large hard drive into 2 partitions. I do this with all my computers. I make a 20 gig opetrating system partition and the rest of the drive isa "D" data partition. This way if i have a problem with Windows i can wipe the "C" partition and reinstall windows easily and never worry about losing the data on the "D" drive.
I use AVG and Avast on different computers had have no problems so far. I alos use the free Zone Alarm firewall and have had no problems with it. I did have some problems with the latest versions of Adobe Acrobat reader but now i use Fox-it reader for PDF files and have deleted all adobe software off my computers.
The only security software made by microsoft i have is what comes with SP2.
The best backup you can get is to buy a CD burner and learn to use it to backup all files you want to save from the computer. This method gives you a permanent backup that will last a long time if you take good care of the cd's. I have programs from 8 years ago that i saved the programs to cd's and now install and run them on my newest computers. I make sure i have at least 2 backups of my important data becaus you never know. One backup is in a safe where even a fire cannot harm it.
Norton Ghost is good if you want to make a recovery type CD or DVD of your system for quick repairs.http://ghost.radified.com/
Something that may be a bit easier to use is Acronis True Image, or Paragon True Image. These are graphical based unlike Ghost which is DOS based.