Prevention of spyware... the same Windows Defender, Spyware Terminator, the aforementioned Spybot, Ad-Aware, AVG Anti-Spyware, a-squared, SpywareBlaster (for IE)... Pretty much you can protect the computer with good free software, or paying some dollars for a little more protection (including trojans and other malware). If you can don't install SpySweeper or Spyware Doctor, not only for the bloat and slowing factor, but for other (possibly paranoid) reasons
About firewalls... you might as well go with the one built in Windows. Seriously, nowadays firewalls are not firewalls, but clumsy "I'll protect you from everything, but you'll get no productivity at all" suites. Maybe I'm being a bit harsh, but for example both Comodo and Outpost carry HIPS modules (very talkative things), and in the case of the latter, they also include the kitchen sink. For now, use a router (until I get my hands onto the subject, it's what I'm using), or light firewalls, if you can find one, of course. Scot Finnie is also conducting a firewall test on his own computers, so check up his website
to see what he recommends. Word of advice: It seems the guy fall in love with methodology used for testing over there at Matousec, which means a firewall is an application monitor, and not a piece software that should prevent the bad guys for getting in there at first.
Or you could as well go with nothing. Yesterday, in the main page of Ars Technica they featured this
discussion about the need of security software, and the conclusions are rather surprising. Who knows? Maybe we're a bit paranoid, but frankly, having to wade through a flood of popups just to have the feeling of security makes me uncomfortable. Probably, it's better to practice safe computing, and stop worrying about the bad guys. Or switch to Linux
. Gizmo is going to kill me if he reads this
And then you read this
other article, it scares the hell out of you, and you put walls around the computer.
One more thing: Layered defense (one application taking care of every type of malware) is better than a multi-layered suite, although this might not be true about Kaspersky.