Try these:

Make sure your network/ router is working (by running something else or running another computer hooked to the router). Boot Knoppix from CD. Confirm that you can not get to the Iinternet by clicking on the knoppix link that shows in the open browser (or use any other working Internet URL). Then open a shell (opps, you didn't tell us which version of Knoppix you're using either; it's the icon with a screen and a shell in front of it in versions 3.3 and eariler, in 3.4 they changed the icon a bit but it still looks like a screen/terminal, it's the one to the right of the little house). type in "sudo mii-tool -r" at the prompt and at the next prompt type "netcardconfig" and go ahead and let it configure by DHCP (DHCP IS enabled in your router, isn't it?).

Also try:
Booting the Knoppix CD and use the EXPERT mode. Answer all questions N. See if the network works when Knoppix comes up.

And finally try:
Boot Knoppix. At the boot prompt enter:


Code:
linux26 acpi=off noscsi
or
Code:
linux24 acpi=off noscsi
if you are running version 3.4 (pick the kernel you wish, either should work fine)

or, if you are using 3.3 or eariler at the prompt type:
Code:
knoppix acpi=off noscsi
Again, see if the network iis now working after Knoppix boots.

Please post back the results of your tests, and if any of these resolve your problem (they have all been discussed in other threads) please let us know what version of Windows is/was install on the computer and if you have installed "security updates".