Norton Internet Security 2005
The bottom line:
Compared to McAfee and ZoneAlarm, Norton Internet Security 2005
isn't as comprehensive. Worse, it may even slow down your
PC.
2005 is already inferior to ZA and even McAfee
I used the 2006 trial for one day, as it still installs the Sym
Common Drivers that Systemworks use. SymEvent for one, and the
ccApp and other processes. And I'm having 512MB RAM.
Not everyone is willing to get a 64-bit Ath X2 system with 2GB ram
just to support that bloated crap.
Technically, if you are up to my specs, any software will work
fine
Then why do people spend days, weeks, months or even years just
to optimize their software? 
So that it will run faster on higher-end systems, and reasonably
fast on lower-powered systems so that the software can be used
technically on every system. Customers do not buy things which lag
their computer down or reduce its performace.
I'm giving up.