I've had this problem on my old computer and now my new one --and have run Adaware, Spybot and using NAV. I'm on comcast cable modem services. When I go into Firefox, generaslly the home page loads fine, I can move between pages easily for a while; after a few minutes, movement is very slow (and/or I get page can't be displayed or not found). I've cleaned out the temp internet files. On my old system I had 512mb RAM, new system 1 gb. On a related issue, I also find myself wondering about changing the cable modem (moto 4100) which is >6 yrs old but seems to have no overt problems and/or the router (netgear 814). I can network w/ my ibook and move around the net well; even on the sites that the desktop says "not found"
I recognize that I may be combining issues, but thoughts, ideas appreciated
thx, alan