I recommend the following after a clean install of Windows 7:
1. Run windows update until there are no more updates available.
2. Install Avast free edition. Update it.
3. Install Mozilla Firefox
4. Install Adblock Plus firefox plugin
5. Install NoScript firefox plugin.
6. Use windows->features->turn windows features on/off to turn off/uninstall IE (internet explorer).
This along with some common sense has kept me virus free for years now.
NoScript can be a pain, as it disables javascript by default for any site you go to but you can easily allow it for sites you visit frequently.
Put yourself in the position of the virus author, nobody is dumb enough anymore to open attachments in email. So you develop websites with trojan javascript code as your virus delivery method. NoScript blocks this by default.
Nothing is free on the internet, except viruses.
