DHCP & self-assigned IP problem-Airport doesn't work

Question

I'm not really a technical type, but I'm pretty quick to pick things up and several weeks of trying to deal with this issue has made me pretty knowledgeable about things related to it specifically.
Background:
I have a month-old Macbook Pro that runs Snow Leopard and is up to date on all its software stuff. On our home network we have another pretty new Macbook Pro running 10.5.9 and a fairly old Macbook also running 10.5.9.
We have a Linksys WRT54G wireless router. Our network uses a 40-bit Hex WEP password.
Problem(s):
When I try to connect to our wireless network, Network preferences tells me that it cannot connect because of a self-assigned IP address. Sure enough, the IP address DHCP comes up with is of the 64.XX.XX.XX variety. Google's revealed that this is a common problem for all recent versions of OSX, back to at least Tiger.
The "subnet mask" it comes up with is 255.255.0.0, which is different from the settings on our other (working) computers, which is 255.255.255.0. I'm not sure what this means, or whether it's significant. Renewing the DHCP lease either comes up with the same 64.XX.XX.XX type or, sometimes, it comes up with no IP settings at all. The most frustrating thing about this is that if I chose "DHCP with manual address" and type in any in our set that I've confirmed isn't in use and hit "apply", as soon as I go back to the panel it has reverted to the 64.XX.XX.XX type.
I've also tried manually entering the router/subnet mask/IP data, as well as the DNS numbers, and that leads to the Network Settings connectivity dot thing being green, but the internet still doesn't work. In those cases, diagnostics claims that everything is fine up to and including the ISP, but that it's unable to connect to the server and internet.
Of note: some people with a similar problem have talked about networks with this problem working intermittently, but mine seems to be consistently broken.
Initially I was able to avoid fixing the problem by using our neighbors' unsecured wireless network, which is sort of awful, I know, but at least it kept me from having to deal with this for a while. Today it started to do the same thing to that network. Both networks continue to work on our Macbook and other Macbook Pro, which is why I don't think that it's a router problem.
I've been able to connect to our other computers through computer-to-computer networks—going through our main shared network (and thus the wireless router) doesn't seem to work—which I think shows that the Airport card/hardware itself is intact (?). I did try connecting to the internet through the "internet sharing" option on our Macbook, but that had the exact same problems.
Another thing that may or may not be relevant, but is equally infuriating:
I've also noticed that my Macbook Pro has more trouble staying connected to a network than our Macbook—even when it was working, it disconnected/timed out extremely often, which is something our Macbook never does, even from the same location. When I try to connect to a network it spends a very long time displaying the "searching for network" animation in the menu bar icon, sometimes after the Network Preferences pane believes that it's connected, and sometimes even after I hit the button to turn Airport off. It's also started refusing to connect to any networks at all, on occasion, which is especially evident in the process of the diagnostics box thingy, because there it actually tells me it's unable to connect rather than just playing the searching animation for ages.
Here are some other things that I've tried:
setting up a new 'location'
restarting the computer
deleting the airport preferences file
restarting in safe mode
restarting open firmware
confirming that the firewall allows all incoming thingies
resetting the router
making sure the keychain password allows all applications to access it
connecting to the internet through a computer-to-computer network from another machine
Because the situation has deteriorated over time, I'd also like to know whether people think that it's two problems (the type of router then later the airport hardware(?)/software(?) itself, perhaps) or just one. Since I've tried basically everything besides switching out our router, I'm kind of inclined to blame it on that, especially because one of the more plausible explanations for this problem that I've heard is a time-out error due to Airport expecting a faster response than it's able to get from older routers; however, the fact that other networks haven't been working means that it's not likely to be just the router. If it's just one problem, which is the simpler explanation, then I guess there's something properly wrong with my computer's software, in which case I guess I'll take it to the Apple Store. :/
I'm in love with my computer otherwise, and I'll admit that I spent a good twenty minutes sobbing out of frustration over this. Any help would be immensely appreciated.

Answer 1

HI and Welcome to Apple Discussions...
Try Changing the Airport Channel
Open AirPort Utility, located in the Utilities folder in the Applications folder on a computer using Mac OS X.
Select the device you’re setting up, and then click Manual Setup. Enter the base station password if necessary
Click AirPort in the toolbar, and then click Wireless.
Choose a new channel from the Channel pop-up menu.
Carolyn