JMRM: Are you still having intermittant connections? Some isp's will check the line/modem to see if there's a problem.

You can do a no. of checks of your connection here: http://www.broadbandreports.com/tools But to get the full range you need to become a paid member. I'm presently an unpaid member. lol

You use a nexswitch SD050s b/w 3 machines. I'm wondering if this requires port forwarding. Are you aware whether it can or not? All I could find was this:
Port forwarding for Unex IS050S which might be similar (same brand.)

I wonder if there's something failing in your network setup.

Have you checked your cable & wiring interfacing/connections to be sure none of them have ben bent or damaged in any way.

I'm not sure about the DNS addresses problems.

Although it's not compulsory to share, you can usually get better dwnlds if people are uplding from you & if you share more than a certain no. of files (some people filter out those that share less than a certain no.)