For some reason, the new operating system, Leopard (Mac OS X 10.5.2), was VERY slow when accessing the Internet. Web pages took minutes to fully load, if at all.
Turns out it was the Ethernet card in the computer. The built in Ethernet port is dead, and the card uses a chipset that does not play well with Leopard.
So I turned on the wireless connection between the computer and the DSL modem/router as an experiment.
And that was it. The card was at fault and the wireless connection is as fast as the previous OS Ethernet connection ever was.
I'll see about getting a new Ethernet card next month, as I prefer a hardwired connection for reasons of security.