99.9999999% of spyware comes because of "I.D. ten Tee" users.
Like when you click yes to the question do u want to install this program by some unknown company.
I've had XP on my laptop with SP 1 for 3 years now. 0 spyware 0 virus. I refuse to upgrade to SP2 because of the firewall.
Some Tip to keep your computer clean.
1. Use webmail. Download attachement from only people u know and only after a online virus scan.
2. Always click no when it prompts to to install something. If you want to install something go to a creditable site and download the exe for it.
3. Don't bother with Firefox(its slow compared to IE, the fastest is opera). Besides If someone wants your computer it does not matter if you are running opera or netscape 1.0, they are going to get into it.
4. The most important one. STOP LOOKING AT PORN
Also
when you get a fresh copy of windows
go to run-> type in msconfig -> start up tab and remember the program. things like Virus scan will be in there too so remember that one as well
when you get a spyware
go to run -> type in msconfig -> start up tab and uncheck any additional suspisious things you find.