Thanks to all of you who offerdd help and wisdom.
I ran Spybot, it found 3 or 4 things the first time, rebooted, ran again, it found 1, repeated, and it now appears clean.
I'm going to get my computer guy to look at it properly for me as I'm useless at these things, meantime I'm going to be using another machine for anything sensitive.
Related, does anyone know how (if possible) to set the router (Belkin ADSL2+ Wireless G) to restrict access to certain sites so that I can prevent my partner, our son and his friends from using Facebook on the network. I've been through the menus and find all sorts of options but there doesn't seem to be one to block a specific site.
I know I can do it on the browsers but we have 4 or 5 computers that are used regularly in the house.