I would increase your RAM at least to 1GB. Meanwhile you can make sure you do not have any McAfee renmamts in your system. Apply MCPR.exe from here: http://mcafee-removal-tool.com/ and reboot your system. Then repair Avast! just in case.

How to repair Avast!
Start > Control panel > Add & Remove programs > select avast! and click " Change/Remove ". Look for " Repair " > Next. Reboot when finnished.