Just revived this to let you know: As SRS and Treewind suggested, I did something about the phone line. Found out that my jack wasn't the master but a slave, my wiring is an ould tyme system (4 not 2 wire) and the line to the master was pretty dirty, with the copper wires oxidised where they make contact (it is wet under the house in winter, but the jack is inside the house.) I cut off the wire and re-made the contacts and disconnected all 3 slave jacks, partly because I couldn't remember how to wire them!
For the last three days I have had no trouble, and long may the situation prevail!
In my own defence I can only say that we had no trouble with the phones at all, and my boy had no trouble for most of the time using my jack, when he did have trouble, he had been using my downloads zip-disk so it looked like a worm or virus.

Like a lot of folk songs, the moral comes last. First, remake the connections of the phone line, which will involve crawling in a crawl space to trace them (reticulation wire to master jack, master jack to slave jack) before you start to throw money at the problem.

Thanks for the suggestions, I'm better equipped to PREVENT problems now, better equipped to CURE problems, and the information I've gleaned is in the paragraph above.

All I need is a harddrive and case to build a whole 400mmx computer out of the bits I changed in the old one.
Except the modem. I'm going to have a business computer that isn't/can't be on the web!   Regards, Chris.