I also had "freezing" and other problems with windows 7 running 3rd part anti-virus and malware programs. Used CC Cleaner and started using the standard Microsoft Security Essentials and have had minimal problems for a year and a half. I'd recommend this path to anyone.
I religiously run quick scans and one a month run a full scan (takes a LONG time).
I have several Toshiba Satellite laptops and have been VERY happy with performance and reliability. I load them up with max RAM to relieve hard drive effort, and haven't had any trouble with whatever video card option I have chosen. You can get a very powerful 8GB main memory equipped Satellite for about $600-700. That price range includes 17" screen models.