My opinion is that if you can renew 2005 and keep that installed, there is less chance of problems. 2006 has a lot more DRM (digital rights management), and tends to have more.... issues. Security is hard, adding DRM makes your head spin as a programmer (been there, done that).
Symantec programmers are generally pretty good, not on a par with ZoneLabs, although good enough, but the executives seemingly have become fixated on anti-piracy and have made Norton top heavy with DRM. It is very difficult to create DRM that does not hurt honest users, and Symantec has failed IMHO.
I try very hard not to disturb Norton on my PCs, since in the last few years too much instability has crept into Norton. When it works well, it is transparent and good for users who want to use the PC without having to monkey with security.
AVG IMHO does not cover as many bases as Norton. It is just too bad that Norton has lost touch with ease of use, I'll be abandoning them when my licenses run out (in, like, 400+ days! Argh!).
Going to SLED 10 using AppArmor. Not for newbies... yet. The final solution is probably something like TPM (trusted computing platform technology). MS will have this around 2050 or so in the meantime, Symantec has a chance to reform itself.