"operation timed out when attempting contact"

I have been getting this error message more frequently.. "the operation timed out when attempting to contact xxxxxxxxxx ". This happens when browsing the net, and/or just reading continuous pages on websites. I have had my service provider check their lines(as I always think it is in their phone lines(still do)), but after they check the lines, and even come into my house, and check, they say it is working fine. The few times a service person has been to my house, I can never duplicate the problem, but seems like as soon as he leaves, the problems re-occur. It doesnt matter which web browser I use, netscape, IE, or Mozilla, I have this problem quite frequently on each one. Does this still sound like a provider problem, or is their some setting on my computer that might solve this delimma?
thanks,
coadman