I just bumped the anti-parasite suite back to the front page. It's a long thread but there are many good suggestions on it. Some are old and some are not. Here is the link to that.
Zone Alarm and Avast are both good tools, To save you some time on the other thread which I would suggest reading anyway, here are some of the ones that are recommended here.
Spybot S&D (download, check for updates, read the tutorial and scan often, it also does some blocking)
SpywareBlaster (a blocker only, download it, check for updates, enable it and leave it alone except for checking for updates occasionally)
SpywareGuard (similiar to SpywareBlaster but works in a different way and does not update as often for that reason.
Ad-Aware SE (a scanner, download, check for updates, read the directions and scan.
cwshredder (stand alone unit)(another small scanner for certain things, ALL other windows should be closed)
I've just bought a new computer and now considering what anti-virus, firewall, spyware to install. I currently have Avast and ZoneAlarm on Windows 98. I know if I trawl through I should find the information (I did find a good thread but had to log off to do something else and now I can't find it!). Any help would be appreciated.