Hi Jessie.
Avast doesn't interfere with LW as far as I know, is it free ?
Here are some of the security programs we recomend
http://www.grisoft.com(good free AVG)
http://www.ewido.com(>>now called AVG Anti Spyware<< free 30 day trial -the best in my opinion)
http://www.lavasoftusa.com/software/adaware/(free)
http://www.ccleaner.com/download/(free)
Spybot - Search & Destroy (FREE)
OK Babe