1. If those are your choices, go with NOD32. It has a much better track record of catching viruses than AVG Free. An alternative free AV is Avast. In terms of commercial products, I do *not* recommend mcafee or symantec. These two programs are bloated and will bring the machine to a crawl. I manage/use eTrust AV 8.x at work and at home. It uses low system resources and is fast.
2. Adaware will not support Vista until Adware 2007 is released (not sure when off the top of my head). SpyBot S&D will not be fully supported until 1.5.
3. Don't have a good answer sorry.
4. Personal preference is for belkin, but linksys definitley works.
5. Go with WPA2. It's backwards compatible for those devices that only support WPA.