I'm sure you probably do all or some of this, yer probably better and smarter than me, but here is what I recommend:

In addition to the Standard Operating Procedures (AV, FW, Etc)

Get a program to wipe and randomize your free space. Wipe the swap file on a semi-regular basis and keep it encrypted. Keep private or sensitive data in a hidden partition, unmounted until you actually NEED to see it (but make sure you MOUNT that puppy before you wipe the free space!!). Wipe the swap after working on sensitive files, and always delete with a file-shredder when a file has reached the end of its life cycle. Wipe FAT/MFT records every now and then.

This will first off insure privacy no matter what nails you. Second, this also sort of 'garbles' some of the areas where bugs like to hide- but no promises... Rule one in the computer profession is that most of us are smart, and many out there are smarter than you, no matter who you happen to be.

Be one of the Alpha Geeks and switch to one of the secure linux OS flavors (thus becoming a target for the next echelon of Alpha++ Geeks, but at least you don't have to worry about the inevitably lucky always malicious skriptkiddies).

Also, in my view, screw trying to work in windows to recover windows- its not going to work. Download a bash emulator like cygwin and find-and-destroy those hidden files that Admin Windows can't even see. You can chown them and -rf them even when Windows can't even see them, and when that fails rename them or chmod them so that the 'black' processes hiding in your memory/cpu cycles can't find what they're looking for and thus crash. You can also mount and umount.

Never trust a disk thats been nailed, and certainly never trust an OS thats been nailed. Do a 9-pass random wipe of the disk and then physically pull the plug on the machine when its done, reformat, and go from there.

But really... Buy a new HD.