Can't Access the WRT54G Router

If 192.168.1.1 isn't the IP address that's configured for the router, it's less of an issue than if the default password isn't correct.
Assuming the Linksys WRT54G you have has been working as your router, you probably have several devices that have been connecting to it.

Find one of those devices and check the IP address configured as the default gateway.

Not sure how to do that?    See How to Find the Default Gateway IP Address for instructions in Windows.