If all your other machines are working fine then the router shouldnt be an issue (Unless there is a limit to how many connections it can have at once. Way to test this, take one machine that works offline, see if you can then pick up an address)
If you are getting a 169 address (Assuming all the others are 192) then the machine isnt receiving a DHCP address from the router. So it points to the USB wireless adapter you have. Have you tried it in another machine? Does it work for anybody else? What are your settings on the wireless? (Dont post them as you dont want your neighbour hijacking your internet
)
With wireless cards/wireless USB devices I have found that sometimes they work with their provided software, sometimes they work better with the built in windows/XP wireless interface. Have you tried to use both?
Try using it on a different machine if you can see what you get there, then you can identify if its the device or a firewall etc.
If it works on other machines, then try to disable the firewalls (As suggested etc) see if that makes a difference. If you can, have a look in the firewall logs, see if its dropping anything.
What are the other wireless devices? G?B? etc.. Is the router transmitting in G? (I have to turn the feature on with mine etc)
Hope that helps to narrow down to what the issue is..