How to get my Linksys ethernet driver loaded into Ubuntu 10.4?

The Linux equivalent of drivers for computers running Windoze(:P) products are called modules and after briefly looking at the Linksys/Cisco website for NIC's, they do not make make drivers/modules specifically for Linux computers. If you're able to browse the web with this ethernet card installed than the Ubuntu operating system found a suitable driver/module to use with the ethernet card to enable your machine to get connected to the Internet.

(You can type this command into a terminal [Application > Accessories > Terminal] "sudo lshw -C network" {w/o the quotes} to see how the operating system recognizes your ethernet card and what driver/module it is using with that device.)

In order to share files with your other computers, you need to tell us if the other computers are using Windoze or Mac or Linux (Ubuntu, Mandriva, etc) as the are different approaches to get a Ubuntu machine to communicate with a Windoze computer or a Mac or another Linux(Ubuntu) computer

Terminal didn't recognize the command, DUH! I've always gotten that message when using terminal, That;s why I like a graphical interface.
As for my other machines, both run Windows XP on hardwire to the Router(Belkin).

lspci -v

Memory at ee082000 (32-bit, non-prefetchable) [size=256]
 Capabilities: <access denied>
 Kernel driver in use: Intel ICH
 Kernel modules: snd-intel8x0

01:0a.0 Ethernet controller: ADMtek NC100 Network Everywhere Fast Ethernet 10/100 (rev 11)
 Subsystem: ADMtek Device 0574
 Flags: bus master, medium devsel, latency 32, IRQ 22
 I/O ports at c000 [size=256]
 Memory at ed000000 (32-bit, non-prefetchable) [size=1K]
 [virtual] Expansion ROM at 30000000 [disabled] [size=128K]
 Capabilities: <access denied>
 Kernel driver in use: tulip
 Kernel modules: tulip

01:0b.0 Modem: PCTel Inc HSP MicroModem 56 (rev 02) (prog-if 01)
 Subsystem: PCTel Inc Device 0001
 Flags: medium devsel, IRQ 19
 I/O ports at c400 [size=64]
 Capabilities: <access denied>
 Kernel driver in use: serial

This is what came up, but it still doesn't help with installing linux drivers(that are not in package form) for it. Below is list of drivers:

LNE100TX v5.1
under linux folder:
copying
netdrv.tgz
readme.txt(instructions via terminal to install to Redhat linux

I stand corrected about Linksys not providing linux drivers/modules for your NIC, I didn't completely read all of your question and I didn't look into the zip file on the Linksys driver page. Could you give the output of these following commands when inputted into a terminal:

dmesg | grep eth
sudo dhclient eth0 (I'm assuming that the logical name for your NIC is eth0, it may be something else, input ifconfig or lshw -C network in a terminal to find out what the logical name is)
sudo ethtool eth0

This following method was suggested by someone who was experiencing a similar issue with this NIC, for some reason the auto detection function was not working.

sudo rmmod tulip (removes the tulip module)
sudo modprobe tulip options=5 (reloads module & forces it to use 100baseTx-FD)

then input "dhclient eth0" (WITHOUT THE QUOTES) in a terminal and hopefully your PC will get an IP address. If it works, you need to make the changes permanent by creating a modprobe.d file, enter the following command in a terminal to do so.

echo 'options tulip options=5' | sudo tee /etc/modprobe.d/tulip.modprobe