Assuming you already set your router and able to connect to net from other pc or os.

What you need to do is setup your networkcard.
Run network card configuration utility, set to use dhcp ( if you set dhcp on router).

If the above doesn't work, hit cancel when asked to use dhcp.
Set IP for your pc, gateway( your router IP ), DNS ( provided by ISP)......etc.

If your setup doesn't stick everytime you boot,read this post:
http://www.knoppix.net/forum/viewtopic.php?t=13636