Hi Walt, nice to hear from you again. I notice you've been registered on the forum for a couple of years now

It's pretty hard to diagnose a problem without actually getting 'hands on' with the PC, and it's somewhat disconcerting that the computer technician you took it to couldn't find anything wrong. All the same, perhaps we can figure something out.
We need to figure out what is causing the slowdown, whether it is the PC itself, the router or your actual internet connection.
1. Check the telephone lineFirst of all (and you might have done this already), you need to contact Karoo when you can't actually connect. Ask them to check the connection on their end, ask them what speed you are getting and if they can see any errors on the line.
2. Check the network connection from router to PCAssuming that Karoo tell you that everything is OK, next we need to eliminate the other end of the connection. When you are having this problem with accessing the Internet, glance down to the bottom right of your screen and see if the icon below (2 computers with a red cross) is displayed.

If it is, this can indicate a problem with the cable, the router, or sometimes with the ethernet (network) socket on the computer itself.
3. Rule out an operating system or software problemFinally, lets try and rule out the operating system (I believe you said you're using Windows XP) or the software installed on it. To totally rule out both Windows and any other software, we can try run Ubuntu on your computer in 'live cd' mode. This mode won't make any changes to your actual hard drive, so won't damage your PC in any way. There is more info here about how to get up and running with live CD mode
https://help.ubuntu.com/community/LiveCDIf you don't get the same problems while using Ubuntu in Live CD mode then you'll know that it is either a problem with Windows or the software you are running. We can then investigate further.