Title says it all. I just installed a fresh copy of Windows XP and the first thing I did was install the drivers for my wireless card. All I get from the network icon is that message: "Windows is unable to find a certificate to log you on to [SSID]"

The pieces of hardware involved are a Linksys Wireless-G WRT54G2 Wireless Router and a more generic Trendnet 802.11g Wireless Ethernet Adapter.

The Network properties say that the network is connected, but there is no Internet connection available.

Through all of this, I've tried a few things, like pinging the router's address. It used to come up with four "Request timed out" messages, but since I reinstalled Windows, now it just says "Destination host unreachable" four times.

Ipconfig shows me an IP address and a subnet mask, but no Default Gateway. This is also the case in the Support tab of the properties of the network.

I also tried swapping out the Trendnet card with another card (a Linksys WMP54G). Usually when Windows asks for a CD to install the drivers from and I put it in, it'll happily install the drivers and all will be fine. However, it said it could not find the drivers. So I installed them manually, and the last dialog box said "The device cannot start." Strange...

Here are various other things I've tried so far with no results (in no particular order):
Reinstalled Windows XP.
Used network card with Windows management and software management (that is, using software from a CD that came with the adapter).
Tried WEP and WPA authentication modes.
Tried different wireless channels.
Disabled Wireless Zero Configuration.

Also, if it's of any use, there are two other computers on the network: one wired to the router, and another connected wirelessly with a Linksys WMP54G (the one I'm using now, not the one with the problem).

All in all, this has been quite a frustrating problem a week in the working. I've tried everything I know how to do, and I'm no networking expert. So anyone with feedback or solutions, I thank you in advance.

Let me know if you need any other information.