OK. A few things.

1) When you tried an alternative card (the Linksys) did you really get
it installed and get all the way to the same point where it's trying
to hook up and it can't get an address? Your description of the test
was so brief it almost implied that you shoved it in -no internet- and
pulled it out. Again, make sure that you get all the way into
hooking up with it and then had exactly the same problem as with the
built-in wireless. That is proof that it's not specific to the one
device.

2) It won't give you an address, but when you start up and then see
the Windows Zero Config (which generally works very well) working, it
DOES see your AP and report it's name and signal strength, right?
Does it show 2 or more bars? Does it indicate that it's unsecured?

3) You say that another pc works on the wireless, but is it in the
same place? More important, have you taken your laptop to the router
and tried getting a connection when you are close to it? This is
important. If it works, then your issue is signal strength or
interference. If it doesn't, then it's configuration or software.

Steve