Daozen & dave.m: I had SS&D, AVG, Windows Def and AD-Aware installed together with absolutely no problem for ages. Just over a couple of years ago the laptop got a virus – can’t remember what it was but it was severe. None of the prevailing amoury was able to detect the problem so I was recommended to try using Avast which I did and it worked perfectly. Then this laptop was stolen and was replaced and, similarly, the software was installed on the new machine with, seemingly, no conflict. Both the previous and current machines are Dell models running XP (Home on prev; Pro on current). My folks have also have a Dell laptop running with similar stuff – never been a sniff of a problem.
My partner uses a Sony Vaio under XP Pro and this machine objected to any more than one of the anti-spyware & anti-virus, as did her previous Compac. I seemed to remember reading on the Dell forums a while ago that Dell stuff is more resilient to using more than one of the above but currently unable to find a link.
Obvious really, but I should point out here that I never run any of this stuff concurrently.
Further to your recommendations I am going to remove AVG. Thanks for the Foxit Reader link, dave. I shall go for that as Adobe is a pain.