hijackthis is also a good tool. It's a bit reliant of you knowing about the inner workings of Windows (e.g. the registry paths), but it's the most robust I can think of.
As for the RAM part: spyware apps don't have to take up huge amounts of memory. Only the amateurish ones really wreck the system and hog resources; the smarter ones only take up a few kilobytes of RAM and are named something important-sounding like "syspip32.exe"
If I were you, I'd back up all my data and reformat the drive. Nuke the site from orbit; that's the only way to make sure.
Myself, I use AVG for anti-virus, and I keep Adaware and Spybot for backup if something funny starts happening. Task Manager/ProcessExplorer to check for errant processes, msconfig.exe to check which apps start up automatically, and regedit if things get dicey. I use Window's built-in firewall; I'm also behind a router which does most of the firewalling for me.