8 gig is good, i know alot of people who are having lots of problem with 4 gig of ram running windows 7.
Weird. I have 3 machines running Win7 x64. One has 8GB of RAM, one has 4GB, and one is an older machine with 2GB. Win7 runs great on all three of them. In fact, it runs better than XP ever did...even on the older machine. The customer service department at our office is full of mahines running Win7 on 1-2GB of RAM and they all run fine.
Also is your pc a pre made or did you get it made to your specs. My sister just got a laptop, win 7 64 bit, 4 gig ram ran like a snail, still testing at the moment, got an idea what the problems are , just need to confirm it. But her anti virus wont load on startup either, even though its enabled, have to go though the whole process during each startup/reboot to start it, its mcafees.
The problem with most laptops is slow hard drives. As the registry and other things that are accessed a lot get bigger they tend to get really slow due to pokey disk I/O. McAfee will only make this worse. Their on-access scan methodology is pretty heavy.
If the OP is having memory issues that's easy to test. You can download one of many boot discs that have diagnostic utilities on them (like http://www.ultimatebootcd.com/) and run Memtest86+ from the boot CD. Let it run over night and see if you get any errors. If the problem is a hardware issue at all it could be anything from heat to a bad HDD cable...there are a lot of possibilities. To me it sounds like a malware issue, though.