I get this occasionally as we have 2 ipods and 2 playstations connecting wireless, and 2 PC connecting wired.
When you get it:
Start, Run, type cmd.exe press <return>
Type ipconfig /release <return>
Then type ipconfig /renew <return>
This will force it to release the IP address and get another one.
When you get the limited or no connectivity message, right click on the network symbol and select Repair.
Just switched from Talk Talk business (nee Freedom 2 Surf) to Sky.