Problem connecting to internet with PC

hello - I hope someone can help me!
I purchased a used computer from my employer. It was "wiped clean", meaning that even the OS was removed (the disks were supplied to us). After getting the unit home, I re-installed the OS (Windows XP Pro, service pack 2).
I then attempted to connect to the internet using a router (Linksys BEFSR41 with 4 ports). My MAC is connected to the router and as you can tell, is working fine. The PC, however, recognizes that it is hooked up to the router, but cannot access the internet.

Obviously I am missing something, just don't know what. I tried the "ping" and provided the IP address for the router, but doing that only gets the following response: Destination host unreachable

I tried advice I saw on this website, just today: Netsh interface set interface name="local area connection" admin=enabled
the response is: An interface with this name is not registered with the router

I am at my wits end, here. very confused and frustrated over this issue. Is there an easy answer? I don't know where to turn.

any advice you can offer is sincerely appreciated!