My operation system is XP. I use Avast Professional to protect my computer against virus, and Windows Defender to protect against Spyware. But my question is , May I use Windows Defender to protect my computer against Adware?
If not, what kind of software I should choose for my PC against Adware?

There is a free adware scanner called AdAware from Lavasoft, its not THE best (I know Spyware Doctor was at some point not sure if thats still true but I don't recommend it anymore) its been more than adequate for my purposes however, so either go find a commercial one or get AdAware (which can also be commercial if you pay for it - gives you realtime protection whereas the free one doesn't, just scanning/removal)

Windows Defender does a pretty good job protecting against both spyware and adware. Basically, adware is a subset of spyware in that it tracks your surfing habits for marketing research.

Windows Defender does a pretty good job protecting against both spyware and adware. Basically, adware is a subset of spyware in that it tracks your surfing habits for marketing research.