The problem appeared on two unrelated laptops at approximately the same
time and I wonder if the problem may be related to Windows update.
When I terminate a wireless phone card connection and switch to
ethernet or when I come back to wireless broadband connection (using
the integrated wireless adapter) after terminating a VPN connection, I
can no longer connect to the internet (no ping response).
When checking with ipconfig, I notice that the terminated connection
(either wireless phone card or VPN) still appears with a default
gateway which is not the default gateway used when the connection was
active but the same default gateway of the now active connection
(ethernet or wireless broadband). This must create a loop which
prevents access to the internet.
Ipconfig renew or release has no effect on the problem which can be
solved only be rebooting the laptop (logging off is not sufficient).

The wireless phone card connection as well as the VPN connection were
created with the WinXP new connection wizard.

I have a Lenovo T43p. The problem appeared when the laptop was in its
original configuration in terms of Lenovo-related utilities (except
windows updates). The problem was not solved by updating the Lenovo
utilities (including Access Connections which I use).

Any hint at a possible solution would be highly welcome.