No Physical Network Connectivity Although Status States Connected?

I would like to know something I have experienced quite often these last couple of weeks at my own offices as well as at some of my clients, on machines all running XP Professional, most with SP3 installed.

Sometimes it happens that only one pc at a time would have no physical connectivity to any outbound services like the internet, or any connection to another pc or the server running SBS 2003 for that matter, although the Network Status in the bottom right hand corner says it is connected, even at 100Mbs.

When opening Network Connections and I view the status of the LAN connection, it shows that packets are being sent and received, but I am not even able to ping another IP on the network, timing out every time.

The only solution to the problem seems to be "repairing" the network connection, and then all works fine again.

I would like to know what might be causing this in the first place and also what exactly a "network connection repair" is actually repairing? The reason I am asking is that I would like to find out if it might be a sign of any hardware starting to malfunction or anything in that regard, so that one could be in the clear about what to possible expect in the future.