i just installed avast on my computer. can avast protect my pc from spyware and adware?
Avast is an antivirus and its main task is to protect your PC from viruses. It can detect some spyware and ad-ware but you should install specialised antimalware to be protected from them. I can advise you to install either Spyware Terminator (http://www.spywareterminator.com/download/download.aspx) or Spybot Search&Destroy (http://www.safer-networking.org/en/home/index.html). They both are free and multilingual.
avast has checkmark accreditation for anti-spyware and is also recognised as an anti-spyware in Vista Security Center.
But it is not a bad idea to have a multi application approach to your security.
If using winXP or Vista SUPERantispyware On-Demand only in free version. Or Spyware Terminator Resident scanner (if you use this don’t install the toolbar or crawler or the anti-virus module).
One of many things I love about Spyware Terminator, is the countdown pop-up in bottom right corner of the monitor, 10 secs before a scheduled scan starts 
Light on resources -about 5mb on my system- and great handling for Safe SoftWare.
Never used SAS though, but since DavidR reccomended it, I will give it a try 
You won’t regret 
Just ran my first scan
I had seen SAS again 1-2 years ago, but the logo reminded me of SpySheriff, which is a malware.
I had a ruff time deleting SpySheriff from my pc then.