Hi. I'll state the issue and then give whatever extra details are needed. I'm running Ubuntu 10.x The Linux box is connected to a router via ethernet. That Linksys router is bridged to an AT&T router.

The bridging is working fine. The AT&T router's page shows the IP of the Linux box and lists it as a device. The Linksys page shows no errors with packet transmission and receipt. I can ping the Linux box from any client on the AT&T router, and can ping the AT&T clients from the Linux box.

I had set the IP of the Linux box to 192.168.1.201 while configuring that router, as I had set that router to 192.168.1.200 and it just seemed orderly. The network preferences show eth0 being set to auto dhcp, but the IP is still set to .201 so I don't know that it actually released or renewed.

When I go into Firefox, it starts in offline mode, and when I switch to online, any request I put in results in spinning until it times out.

To troubleshoot some more info is needed. For a start, post output of
# ifconfig
# route
# cat /etc/resolv.conf

ifconfig

eth0 Link encap:Ethernet HWaddr 00:0d:60:70:bb:df
inet addr:192.168.1.201 Bcast:192.168.1.255 Mask:255.255.255.0
inet6 addr: fe80::20d:60ff:fe70:bbdf/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:1046087 errors:0 dropped:0 overruns:0 frame:0
TX packets:1023376 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:100
RX bytes:119003941 (119.0 MB) TX bytes:82183813 (82.1 MB)

lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
inet6 addr: ::1/128 Scope:Host
UP LOOPBACK RUNNING MTU:16436 Metric:1
RX packets:3343 errors:0 dropped:0 overruns:0 frame:0
TX packets:3343 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:614402 (614.4 KB) TX bytes:614402 (614.4 KB)

-----------
route

Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
192.168.1.0 * 255.255.255.0 U 0 0 0 eth0

-----------
etc/resolv.cfg

nameserver 192.168.1.1

Ok, you have no default route, I don't know if your dns-server is correct.
Try restarting network, should be a gui for that or issue command:
#/etc/init.d/networking restart

Fixed! There wasn't a gui for restarting the network, but while looking around the edges of the screen for something, I found an icon that looks like a transmitting antenna, and it was red. When I clicked on it, it said that no device was assigned and no connection, and it listed the ethernet connection, so I clicked it and voila! Is this something that I will need to do regularly?

Thanks! I started with a Linksys router that I had to flash with a new o/s to make it a bridge ... it's been a long couple days!!

No, you will not need to do that regularly.
It happened because you manually set an ip, but as you're using dhcp from now on nic gets adress automatically - including correct route & dns.