superantispyware free is ON Demand- it has no free shield
in General Spybot is the same - a scanner
With Spybot I update my Host File every wednasday and then update Spybot and re-immunize with spybot
(My host updater wipes out Spybot's hosts enteries- so they get added back- I also could use Hoster but not worth the effort)
SPybot has two prevention aids besides immunization
the first is SD-Helper which helps protect Internet Explorer
The Second is Spybot T-timer which protects the registry and recently loads a list of baddies (which takes some time when first accessed) to check against
There is NO FREE LUNCH however T-Timer is one of the very few free anti-spyware real time tools
T-timer has a new (beta) update for low memory systems
I also run Win-Patrol
To answer your question
I run whatever Avast Shields are available
Standard, E-Mail, Web I do not use P2P so it's off as is Outlook etc
your other question
you can go to BlackVipers website and use his XP configuration tool to slim down xp and also do not let Anything start at start up that you do not need at startup-like adobe, office blah blah blah
some of these things can really chew up your memory
load them when you need them- a little longer load then vs a slower system all the time
what's not to like?
your other question
once you are clean I'd run CCleaner, Dfrag and delete and set new restore points