Odd problem with Vista wireless network

[Achilles]

I set up a wireless network on a linksys router using my dell laptop which has vista. It works fine for all systems that have vista (only tested on my computer and my brothers). However, I tried to hook up my brothers desktop (which has a wireless card that has worked previously and I think it's working now) and it won't connect. It gives a message saying it was unable to identify a certificate. This message pops up after it tries to connect for a while right after I enter the key.

Any ideas?

[glc]

You may be using an advanced encryption method that's not compatible with earlier operating systems.

[Achilles]

Would there be any way to change that? I'm guessing no, unless I completely reinstall the router on the xp computer...

[glc]

Routers do not have to be "installed" on any computers. You administer the router through its Web interface. You browse to its IP address and log in with a wired computer.

If all computers have XP with SP2 or SP3 or Vista, my recommended encryption is WPA-PSK using the AES algorithm. If older operating systems are involved, you may have to use 128 bit WEP instead.

As a TEST, you can turn encryption OFF and see if all computers can connect.