You need to install and update:
1. A resident Anti-virus (check of updates to definitions daily)
2. A resident firewall (only update when new versions come out)
3. At least two spyware applications (check for definition updates daily)
Free applications for the above can be found at BC:http://www.bleepingcomputer.com/forums/topic3616.html
(I use and recomment AVG anti-virus, Sygate Personal Firewall, and both Ad-AwareSE as well as Spybot Seach and Destroy, all of which are linked at the above)
The following tutorials are recommended:http://www.bleepingcomputer.com/tutorials/safely-connecting-a-computer-to-the-internet/http://www.bleepingcomputer.com/tutorials/understanding-spyware-browser-hijackers-and-dialers/http://www.bleepingcomputer.com/tutorials/keep-your-computer-safe-online/
These will give you a start. There are also tutorials on using these applications.
There is also a beginning HiJackThis! tutorial. This may help you understand and interpret your log.