I've had problems getting any NIC card to run in the top slot on my Dell Inspiron 7000, the Linksys was no exception. After I moved the card to the bottom slot on the laptop the install went smooth enough. Follow the directions in the quick installation page to the letter and you shouldn't have too many problems. The last time I saw that error while testing a NIC it was in half duplex mode at 100 Mb. Sure enough my Cisco 1548 switch indicated that the NIC was in half duplex mode.
Full duplex means that the card can transmit and receive at the same time.
Half duplex means that the card can transmit or receive, but it cannot do both at the same time. That's right, no full duplex operation at 100Mb. A little disappointing though, because I had to drop the card down to 10 Mb full duplex to test it, because that was the fastest speed I could set the card to without getting an error. I then set the card back to auto sense, rebooted, verified that the card was in 100 Mb mode on the switch, and then transferred a 10.9 MB file across my home LAN in 13 seconds. If you use IE 5.0 or higher, all menus and ads are automatically removed when you print a page.